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Year 10 General Maths Unit 2 Topic 2 Linear Growth and Decay Page 1 of 20 Year 10 General Mathematics Unit 2 Financial Arithmetic II Topic 2 – Linear Growth and Decay In this area of study students cover mental, byhand and technology assisted computation with rational numbers, practical arithmetic and financial arithmetic, including estimation, order of magnitude and accuracy. This topic includes: applications of simple interest and compound interest cash flow in common savings and credit accounts including interest calculation compound interest investments and loans Key knowledge concepts of simple and compound interest and their application compound interest investments and debts. Key skills apply simple interest to analyse cash flow in common savings and credit accounts apply compound interest to solve problems involving compound interest investments and loans compare the costs of a range of purchase options such as cash, credit and debit cards, personal loans, and time payments (hire purchase). Chapter Sections Questions to be completed 1. Simple Interest Tables In the notes (4 questions) 2. Simple Interest Formula (3.5 Textbook) 1bd, 2bd, 3bd, 4bd, 12, 13, 16 3. Simple interest Loans (3.5 Textbook) 5bd, 8, 10, 14, 17, 20, 22 4. Simple Interest – Recurrence relation In the Notes (3 questions) 5. Simple interest – General recurrence relation In the Notes (5 questions) 6. Flat rate depreciation In the Notes (5 questions) 7. Unitcost depreciation In the Notes (3 questions) More resources available at http://drweiser.weebly.com

Transcript of Year%10%General%Mathematics%% Unit%2%6 ...€¦ · Year%10General%Maths%Unit%2% %...

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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Year  10  General  Mathematics    Unit  2  -­‐  Financial  Arithmetic  II  Topic  2  –  Linear  Growth  and  Decay  In  this  area  of  study  students  cover  mental,  by-­‐hand  and  technology  assisted  computation  with  rational  numbers,  practical  arithmetic  and  financial  arithmetic,  including  estimation,  order  of  magnitude  and  accuracy.  This  topic  includes:  •   applications  of  simple  interest  and  compound  interest  •   cash  flow  in  common  savings  and  credit  accounts  including  interest  calculation  •   compound  interest  investments  and  loans  Key  knowledge  •   concepts  of  simple  and  compound  interest  and  their  application  •   compound  interest  investments  and  debts.  Key  skills  •   apply  simple  interest  to  analyse  cash  flow  in  common  savings  and  credit  accounts  •   apply  compound  interest  to  solve  problems  involving  compound  interest  investments  and  loans  •   compare  the  costs  of  a  range  of  purchase  options  such  as  cash,  credit  and  debit  cards,  personal  loans,  

and  time  payments  (hire  purchase).      

 

Chapter  Sections   Questions  to  be  completed  

1.  Simple  Interest  Tables   In  the  notes  (4  questions)  

2.  Simple  Interest  Formula  (3.5  Textbook)   1bd,  2bd,  3bd,  4bd,  12,  13,  16  

3.  Simple  interest  -­‐  Loans  (3.5  Textbook)   5bd,  8,  10,  14,  17,  20,  22  

4.  Simple  Interest  –  Recurrence  relation   In  the  Notes  (3  questions)  

5.  Simple  interest  –  General  recurrence  relation   In  the  Notes  (5  questions)  

6.  Flat  rate  depreciation   In  the  Notes  (5  questions)  

7.  Unit-­‐cost  depreciation   In  the  Notes  (3  questions)      

More  resources  available  at  

http://drweiser.weebly.com  

 

 

   

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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Table  of  Contents    

1.  SIMPLE  INTEREST  TABLES  ................................................................................................................................  3  SIMPLE  INTEREST  ...................................................................................................................................................  3  

EXAMPLE  1.1  .....................................................................................................................................................................................  3  EXAMPLE  1.2  .....................................................................................................................................................................................  4  

EXERCISE  1.  ..........................................................................................................................................................  4  

2.  SIMPLE  INTEREST  FORMULA  ............................................................................................................................  5  EXAMPLE  2.1  .....................................................................................................................................................................................  5  

FINDING  VO,  R  AND  N  ..............................................................................................................................................  5  EXAMPLE  2.2  .....................................................................................................................................................................................  5  EXAMPLE  2.3  .....................................................................................................................................................................................  6  WORKED  EXAMPLE  9:  ..........................................................................................................................................................................  6  

3.  SIMPLE  INTEREST  -­‐  LOANS  ...............................................................................................................................  7  WORKED  EXAMPLE  3.1  ........................................................................................................................................................................  7  

CASH  FLOW  ..........................................................................................................................................................  7  NON-­‐ANNUAL  INTEREST  CALCULATIONS  .................................................................................................................  7  

WORKED  EXAMPLE  3.2  ........................................................................................................................................................................  7  MINIMUM  BALANCE  CALCULATIONS  .....................................................................................................................  8  

WORKED  EXAMPLE  3.3  ........................................................................................................................................................................  8  

4.  SIMPLE  INTEREST  -­‐  RECURSION  RELATION  ...........................................................................................................  9  EXAMPLE  4.1  RECURRENCE  RELATION  ......................................................................................................................................................  9  

SIMPLE  INTEREST  USING  CAS  CALCULATOR  ...............................................................................................................  10  EXAMPLE  4.2  ...................................................................................................................................................................................  10  EXAMPLE  4.3  ...................................................................................................................................................................................  11  

EXERCISE  4.  MODELLING  SIMPLE  INTEREST  WITH  RECURRENCE  RELATIONS  .....................................................................  12  

5.  GENERAL  RECURRENCE  RELATION  FOR  THE  NTH  TERM  IN  LINEAR  GROWTH.  ...............................................................  13  EXAMPLE  5.1  USING  A  RULE  TO  DETERMINE  THE  VALUE  OF  A  SIMPLE  INTEREST  INVESTMENT  ...............................................................................  14  EXAMPLE  5.2  ...................................................................................................................................................................................  14  

EXERCISE  5  .........................................................................................................................................................  15  

6.  FLAT  RATE  DEPRECIATION  ..............................................................................................................................  16  FLAT  RATE  (STRAIGHT  LINE  DEPRECIATION)  ...............................................................................................................  16  

EXAMPLE  6.1  ...................................................................................................................................................................................  16  EXERCISE  6  .........................................................................................................................................................  18  

7.  UNIT-­‐COST  DEPRECIATION  .............................................................................................................................  19  UNIT  COST  DEPRECIATION  RECURRENCE  RELATION  .....................................................................................................  19  

EXAMPLE  7.1  ...................................................................................................................................................................................  19  EXERCISE  7  .........................................................................................................................................................  20  

     

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1.  Simple  Interest  Tables  When  you  borrow  money  from  a  bank  or  financial  institution,  taking  out  a  loan  or  mortgage  (a  home  loan),  you  must  repay  the  original  amount  borrowed  plus  an  extra  amount  you  are  charged  for  using  the  banks  money.  This  “extra”  amount  is  called  interest.  

Similarly,  if  you  put  money  into  a  bank  (i.e.  a  savings  account),  you  are  paid  by  the  bank  for  letting  them  use  your  money.  The  money  you  are  paid  is  the  interest.    

(The  money  you  put  in  the  bank  is  used  by  the  bank  to  loan  out  to  other  people  and  other  investments.)  

There  are   two  common  ways   that   interests  are  calculated,   they  are  known  as  Simple   Interest   and  Compound  Interest.  In  this  section,  we  will  only  be  concerned  with  Simple  Interest.  We  will  investigate  Compound  Interest  later.  

Simple  Interest  

If  you  invest  or  borrow  money  from  the  bank  and  you  are  reward  or  charged  a  fixed  amount  of  interest  at  regular  time  periods  it  is  called  a  Simple  Interest.  

Simple  Interest  is  an  example  of  linear  growth  where  the  interest  is  usually  calculated  as  a  percentage  of  the  amount  invested  or  borrowed,  the  starting  value  (V0)  or  Principal.  This  constant  amount  is  added  at  each  payment  over  the  duration  of  the  loan.  Simple  interest   involves  a  calculation  based  on  the  original  amount  borrowed  or  invested;  as  a  result,  the  amount  of  simple  interest  for  the  duration  of  loan  is  constant.  For  this  reason,  simple  interest  is  often  called  flat  rate  interest.  

Example  1.1  

John  invests  $5  000  into  a  bank  to  save  for  his  first  car.  The  bank  gives  him  4  %  interest  per  year.  Using  simple  interest,  calculate  how  much  money  will  he  have  after  5  years  if  interest  was  to  be  calculated  yearly?  

Principal  =  Amount  invested  =    _________________________________________________    

Interest  rate  =     _____________________________________________________________    

Time/Period  invested  =    ______________________________________________________    

Time   Principal   Interest   Interest  Accumulation  

1        

2        

3        

4        

5        

 

Total  interest  earnt  after  5  years  =    __________________________________________________    

Total  amount  earnt  =    _____________________________________________________________      

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Example  1.2    

Kayla  borrows  $3  000  from  a  bank  to  put  towards  her  savings  for  her  oversea  trip.  The  bank  lends  her  for  a  period  of  18  months  with  an  interest  rate  of  7.8%  pa.  Using  simple  interest,  how  much  does  she  owe  after  18  months  if  the  interest  is  calculated  quarterly?  

Interest  rate  =     _____________________________________________________________    

Time/Period  borrowed  =    _____________________________________________________    

Time   Principal   Interest   Interest  Accumulation  

1        

2        

3        

4        

5        

6        

Total  interest  owed  =    ________________________________________________________    

Total  amount  of  money  Kayla  owed  =    ___________________________________________    

 Exercise  1.  

1.   For  the  following  questions  use  a  table  to  calculate:  i   the  amount  of  simple  interest,  I,  earned  ii   the  total  amount,  A,  at  the  end  of  the  term.  

(a)   $1200  for  5  years  at  10.5%  p.a.  calculated  yearly.  (b)   $8320  for  3  years  at  6.45%  p.a.  calculated  quarterly.  (c)   $960  for  1  ½  years  at  9.20%  p.a.  calculated  monthly.  

 2.   Calculate  the  simple  interest  that  has  to  be  paid  if  $4  650  is  invested  on  term  deposit  for  7  years  

at  5.75%  p.a.  

 3.   Jenny  wishes  to  invest  $3  500  for  2  years  at  4.95%  p.a.  but  is  not  quite  sure  which  option  will  give  

her  the  ultimate  reward.  Calculate  the  return  for  each  of  the  investment  and  advice  Jenny  which  option  is  best  for  her.    (a)   annually  (b)   half-­‐yearly  (c)   monthly  

 4.   For  the  following  questions  use  CAS  calculator  to  calculate  the  total  amount,  A,  owed  at  the  end  

of  the  term  when  borrowing:  (a)  $18  400  for  10  years  at  6.89%  p.a.  calculated  yearly.  (b)  $2460  for  4  years  at  5.75%  p.a.  calculated  quarterly.  (c)   $3730  for  4 #

$  years  at  7.39%  p.a.  calculated  monthly.  

(d)  $126  000  for  3  years  at  8.35%  p.a.  calculated  daily.      

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2.  Simple  Interest  Formula  By  obse0rving  how  simple  interest  is  calculated  from  the  above  table,  we  can  see  that  under  the  Interest  Accumulation  column  it  follows  a  general  rule:  

Simple  Interest  =  𝐼 = 𝑉(×*+((

×𝑛 = -.*/+((

 Where     I  =  the  amount  of  interest  earned,  or  owed  ($)       V0  =  Principal  –  the  starting  amount  of  money  invested  or  borrowed  ($)       r  =  Rate  of  the  interest  per  year  or  per  annum  (p.a.)  (%)       n=  Term  -­‐  borrowed  or  investment  period  (could  be  years,  quarters1,  months,  fortnights2)    Example  2.1  Calculate  the  amount  of  simple  interest  earned  on  an  investment  of  $4450  that  returns  6.5%  per  annum  for  3  years.            Finding  Vo,  r  and  n  We   can   rearrange   the   simple  interest   formula   to   find   the   initial  amount  or  principal  (𝑉(),  the  interest  rate   (𝑟)   or   the   term   of   the   loan   or  investment  (𝑛)  

 

Example  2.2  A  bank  offers  4.5%  p.a.  simple  interest  on  an  investment.  At  the  end  of  4  years  the  total  interest  earned  was  $90.  How  much  was  invested?  Example  2.2  on  CAS  calculator  On  a  calculator  use  the  nSolve  function,      Enter  the  equation  𝐼 = -1×*×/

+((, 𝑉(  

 and  set  the  values  of  𝐼, 𝑟  𝑎𝑛𝑑  𝑛    using  “|”,  I=$90,  r=4.5  and  n=4  

 

                                                                                                                         1  A  quarter  of  a  year  is  ¼  x  12  months  =  3  months  2  A  fortnight  is  2  weeks,  there  are  26  fortnights  in  a  year  (52  weeks  in  a  year/2  =  26)  

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Example  2.3  

What  simple  interest  rate  is  required  to  earn  $86.70  interest  on  an  original  amount  of  $255  in  4  years?  

 

 

 

 

Example  2.3  on  CAS  calculator  On  a  calculator  use  the  nSolve  function,    

 

Enter  the  equation  𝐼 = -1×*×/+((

,    

and  set  the  values  of  V0  ,  I  and  r  using  “|”,  I=$86.70,  V0=255  

and  n=4.  

   

Worked  Example  9:  

How  long  will  it  take  an  investment  of  $2500  to  earn  $1100  with  a  simple  interest  rate  of  5.5%  p.a.?  

 

 

 

 

   

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3.  Simple  Interest  -­‐  Loans  At  the  end  of  the  borrowing  or  investing  period,  the  total  amount  of  money  repaid  or  awarded  to  you  is  calculated  as  followed.  

Amount  =  Principal  +  Interest  Where       A  =  Total  Amount  repaid  or  reward  ($)  

      P  =  Principal  ($)  or  starting  amount         I  =  Simple  Interest  ($)  

 

Worked  Example  3.1    

Calculate  the  monthly  payments  for  a  $14  000  loan  that  is  charged  simple  interest  at  a  rate  of  8.45%  p.a.  for  4  years.  

 

 

 

 

 

 

 

 

Cash  flow  

Non-­‐annual  interest  calculations  

Although  interest  rates  on  investments  and  loans  are  frequently  quoted  in  terms  of  an  annual  rate,  calculations  on  interest  rates  are  made  more  frequently  throughout  a  year.  Quarterly,  monthly,  weekly  and  even  daily  calculations  are  not  uncommon.  

 

Worked  Example  3.2  

How  much  interest  is  paid  on  a  monthly  balance  of  $665  with  a  simple  interest  rate  of  7.2%  pa?  

 

 

 

 

   

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Minimum  Balance  Calculations  

Banks  and  financial  institutions  need  to  make  decisions  about  when  to  apply  interest  rate  calculations  on  accounts  of  their  customers.  For  investment  accounts,  it  is  common  practice  to  use  the  minimum  balance  in  the  account  over  a  set  period  of  time.    

Worked  Example  3.3  

Interest  on  a  savings  account  is  earned  at  a  simple  rate  of  7.5%  p.a.  and  is  calculated  on  the  minimum  monthly  balance.  How  much  interest  is  earned  for  the  month  of  June  if  the  opening  balance  is  $1200  and  the  following  transactions  are  made?  Give  your  answer  correct  to  the  nearest  cent.  

Date   Details   Amount  June  2   Deposit   $500  June  4   Withdraw   $150  June  12   Withdraw   $620  June  18   Deposit   $220  June  22   Withdraw   $500  June  29   Deposit   $120  

 Date   Details   Withdraw   Deposit   Balance  June  1   Opening  Balance        June  2   Deposit     $500    

June  4   Withdraw   $150      

June  12   Withdraw   $620      

June  18   Deposit     $220    

June  22   Withdraw   $500      

June  29   Deposit     $120    

     

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4.  Simple  Interest  -­‐  Recursion  Relation  Simple  interest  can  be  represented  by  a  first-­‐order  linear  recurrence  relation.  

 You  can  also  calculate  the  total  amount  of  a  simple  interest  loan  or  investment  by  using:    

 where:  

 In  the  case  of  simple  interest,  the  total  value  of  investment  increases  by  the  same  amount  per  period.  Therefore,  if  the  values  of  the  investment  at  the  end  of  each  time  period  are  plotted,  a  straight-­‐line  graph  is  formed.    

Example  4.1  Recurrence  relation  

Example  2  can  be  approached  using  recurrence  relations,  where  Vn  is  the  amount  owed  at  the  end  of  the  nth  period  and  Vn+1  is  the  amount  owed  in  the  next  period.  

Kayla  borrows  $3  000  from  a  bank  to  put  towards  her  savings  for  her  oversea  trip.  The  bank  lends  her  for  a  period  of  18  months  with  an  interest  rate  of  7.8%  pa.  Using  simple  interest,  how  much  does  she  owe  after  18  months  if  the  interest  is  calculated  quarterly?  

 

 

n  +  1   Vn   Balance  at  the  end  of  n  +  1  time  (Vn+1)  

1   V0  =     V1  =  

2   V1  =   V2  =  

3   V2  =   V3  =  

4   V3  =   V4  =  

5   V4  =   V5  =  

6   V5  =   V6  =    

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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Simple  Interest  using  CAS  calculator  

Example  4.2    

Jan  invests  $210  with  building  society  in  a  fixed  deposit  account  that  paid  8%  p.a.  simple  interest  for  18  months.  a)  How  much  did  she  receive  after  the  18  months?  

•   Step  1.  Make  sure  𝑟  and  𝑛  are  in  the  same  units  

 

 

 

 

 

 

Example  4.2  on  CAS  Calculator  (calculator  page) Start  with  a  blank  calculator  page  Press  •   Type  210  •   press  enter  

·

Next  type  +1^40

Press  enter  ·

Note:  when  you  press  enter,  the  CAS  converts  ANS  to  the  value  of  the  previous  answer  (in  this  case  210)

 

Pressing  ·  repeatedly  applies  the  rule  “+1.40”  to  the  last  calculated  value,  in  the  process  generating  the  amount  of  the  investment  at  the  end  of  each  year  as  shown.

 

 

 

1st  year  

2nd  year  

3rd  year  

4th  year  

5th  year  

 

After  18  months  of  investment,  Jane  will  receive    __________________________________    

   

Initial  Value  V0  

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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b)  Represent  the  account  balance  for  each  of  the  18  months  graphically.  

Example  on  CAS  Calculator  (Lists  and  Spreadsheet  Page) Label  column  A  “month”  Enter  0  in  cell  A1  In  cell  A2  enter:  =a1+1  Fill  down  until  the  18th  month    

 

Label  column  B  “total”  Enter  $210  in  cell  b1  In  the  next  cell  (B2)  enter  the  equation    

=210+1.4  x  a2  

 

Now   fill   down   this   equation   to   the  cells  below.  Press  Menu  b,  data  3,  fill  3    

   Add  a  data  and  statistics  page  /~    Put  the  “month”  on  the  x  axis    and  “total”  on  the  y  axis        

 Example  4.3  

$1000  is  invested  in  a  simple  interest  account  for  5  years  at  5.5%  p.a.    a)   Set  up  a  recurrence  relation  to  find  the  value  of  the  investment  after  n  years.  

 

 

 

 

 

 

b)   Use  the  recurrence  relation  from  part  (a)  to  find  the  value  of  the  investment  at  the  end  of  each  of  the  first  5  years.  

n   Vn($)   Vn+1  ($)  0   V0  =  1000   -­‐  

1      

2      

3      

4      

5  

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Exercise  4.  Modelling  simple  interest  with  recurrence  relations    

1.  The   following   recurrence   relation   can   be   used   to  model   a   simple   interest   investment   of   $2000  paying  interest  at  the  rate  of  3.8%  per  annum.  V0  =2000,  Vn+1  =Vn  +76  In  the  recurrence  relation,  Vn  is  the  value  of  the  investment  after  n  years.    

a)   Use  the  recurrence  relation  to  find  the  value  of  the  investment  after  1,  2  and  3  years.    

b)   Use  your  calculator  to  determine  how  many  weeks  it  takes  for  the  value  of  the  investment  to  be  more  than  $3000.    

c)   Write  down  a  recurrence  relation  model  if  $1500  was  invested  at  the  rate  of  6.0%  per  annum.    

2.  The  following  recurrence  relation  can  be  used  to  model  a  simple   interest   loan  of  $7000  charged  interest  at  the  rate  of  7.4%  per  annum.  V0  =7000,Vn+1  =Vn  +518  In  the  recurrence  relation,  Vn  is  the  value  of  the  loan  after  n  years.    

a)   Use  the  recurrence  relation  to  find  the  value  of  the  loan  after  1,  2  and  3  years.  

b)   Use  your  calculator  to  determine  how  many  weeks   it  takes  for  the  value  of  the   loan  to  be  more  than  $10  000.    

c)   Write  down  a   recurrence   relation  model   if   $12000  was  borrowed  at   the   rate  of   8.2%  per  annum.  

3.   The  following  recurrence  relation  can  be  used  to  model  a  simple  interest  investment.  In    

the  recurrence  relation,  Cn  is  the  value  of  the  loan  after  n  years.  C0  =15000,  Cn+1  =Cn  +525    

a)   i  What  is  the  principal  of  this  investment?  

ii  How  much  interest  is  paid  every  year?    

iii  What  is  the  annual  interest  rate  of  this  investment?    b)   Use  your  calculator  to  determine  how  many  weeks  it  takes  for  the  value  of  the  investment  to  

be  more  than  double  the  principal.    

   

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5.  General  recurrence  relation  for  the  nth  term  in  linear  growth.    

While  we  can  generate  as  many  terms  as  we  like  in  a  sequence  using  a  recurrence  relation  for  linear  growth  and  decay,  it  is  possible  to  derive  a  rule  for  calculating  any  term  in  the  sequence  directly.  This  is  most  easily  seen  by  working  with  a  specific  example.    

For  instance,  if  you  invest  $2000  in  a  simple  interest  investment  paying  5%  interest  per  annum,  your  investment  will  increase  by  the  same  amount,  $100,  each  year.    

If  we  let  Vn  be  the  value  of  the  investment  after  n  years,  we  can  use  the  following  recurrence  relation  to  model  this  investment:    

V0  =2000,  Vn+1  =Vn  +100  

Using  this  recurrence  relation,  we  can  write  out  the  sequence  of  terms  generated  as  follows:    

V0  =  2000     =  V0  +0×100     (no  interest  paid  yet)    

V1  =  V0  +  100     =  V0  +1×100     (after  1  years’  interest  paid)    

V2  =V1  +100=(V0  +100)  +100     =  V0  +2×100     (after  2  years’  interest  paid)    

V3  =V2  +100=(V0  +2×100)  +100     =  V0  +3×100     (after  3  years’  interest  paid)    

V4  =V3  +100=(V0  +3×100)  +100     =  V0  +4×100     (after  4  years’  interest  paid)    

and  so  on.  

Following  this  pattern,  after  n  years’  interest  has  been  added,  we  can  write:    

Vn  =2000+n×100  

With   this   rule,  we   can   now   predict   the   value   of   the  nth   term   in   the   sequence  without   having   to  generate  all  the  other  terms  first.  This  rule  can  be  readily  generalised  to  apply  to  any  linear  growth  or  decay  situation.  For  a  recurrence  rule  of  the  form:V0  =  initial  value,  Vn+1  =  Vn  +  d  (d  is  constant)  the  value  of  the  𝑛th  term  generated  by  this  recurrence  relation  is:  

𝑉/ = 𝑉( + 𝑛×𝑑, where  𝑑 =𝑉(𝑟100  

where   V0  is  the  initial  value  of  the  investment  or  loan,  

  r  is  the  rate  of  depreciation  per  year  

Note  that  the  starting  Value  V0  must  always  be  stated  also.    

   

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Example  5.1  Using  a  rule  to  determine  the  value  of  a  simple  interest  investment    The  following  recurrence  relation  can  be  used  to  model  a  simple  interest  investment:    

V0  =3000,  Vn+1  =Vn  +260

where  Vn  is  the  value  of  the  investment  after  n  years.    

a)   What  is  the  principal  of  the  investment?  How  much  interest  is  added  to  the  investment  each  year?  

       

b)   Write  down  the  rule  for  the  value  of  the  investment  after  n  years.  

 

 

 

 

c)   Use  a  rule  to  find  the  value  of  the  investment  after  15  years.  

 

 

 

 

d)   Use  a  rule  to  find  when  the  value  of  the  investment  first  exceeds  $10000.    

 

       Example  5.2  

Amie  invests  $4000  in  a  simple  interest  investment  of  paying  interest  at  the  rate  of  6.5%  per  year.  Use  a  rule  to  find  the  value  of  the  investment  after  10  years.    

   

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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Exercise  5  

1.   Write  down  a  rule  for  the  value  of  the  nth  term  of  the  sequence  generated  by  each  of  the  following  recurrence  relations.  In  each  case  calculate  A20.    

a)  A0  =  4,  An+1  =  An  +  2   b)  A0  =10,  An+1  =An  +3  

c)  A0  =  5,  An+1  =  An  +  8 d)  A0  =300,  An+1  =An+18

 

2.     The  value  of  a  simple  interest  loan  after  n  years,  Fn,  can  be  calculated  from  the  rule:  

Fn  =  8000  +  512n  

a)   What  is  the  principal  of  this  loan?    

b)   How  much  interest  is  charged  every  year  in  dollars?    

c)   Use  the  rule  to  find:   i)  the  value  of  the  loan  after  5  years  ii)  how  long  it  takes  for  the  initial  investment  to  double.    

d)   The  annual  interest  rate  for  this  loan  is  6.4%.  Use  this  information  to  find  the  value  of  the  loan  after  15  years.    

3.  The  value  of  a  simple  interest  investment  after  n  years,  Vn,  can  be  calculated  from  the  rule:    

Vn  =  2000  +  70n.  

a)   How  much  interest  is  awarded  every  year  in  dollars?    

b)   Use  the  rule  to  find:    i)  the  value  of  the  investment  after  6  yearsii)  how  long  it  takes  for  the  initial  investment  to  double.  

c)   The  annual  interest  rate  for  this  loan  is  3.5%.  Use  this  information  to  find  the  value  of  the  loan  after  10  years.    

4.     Webster  borrows  $5000  from  a  bank  at  an  annual  simple  interest  rate  of  5.4%.    

a)   Determine  how  much  interest  is  charged  each  year  in  dollars.

b)   Write  down:  i  a  recurrence  relation  to  model   the  value  of   the   loan,  Vn,   from  year  to  year       ii  a  rule  for  the  value  of  the  loan,  Vn,  after  n  years.

c)   Use  your  rule  in  part  b)  ii)  to  find  how  much  Webster  will  owe  the  bank  after  9years.    

5  Anthony  borrows  $12  000  from  a  bank  at  an  annual  simple  interest  rate  of  7.2%.    

a)   Determine  how  much  interest  is  charged  each  year  in  dollars.

b)   Write  down:     i  a  recurrence  relation  to  model  the  value  of  the  loan,  Bn,  from  year  to  year    

ii  a  rule  for  the  value  of  the  loan,  Bn,  after  n  years.    

c)  Use  your  rule  in  part  b)  ii)  to  find  how  much  Anthony  will  owe  the  bank  after  11  years.    

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6.  Flat  rate  depreciation  Some  items  such  as  antiques,  jewellery  and  real  estate  increase  in  value  (appreciate  or  increase  in  capital  gain.  Computers,  mobile  phones,  cars  or  machinery  decrease  in  value  (depreciate)  with  time  due  to  wear  and  tear,  advances  in  technology  or  lack  of  demand.  Depreciation  is  the  estimated  loss  in  value  of  assets.  The  estimated  value  of  an  item  at  a  point  in  time  is  called  its  future  value  (book  value).  

When  the  value  becomes  zero,  the  item  is  written  off.    

At  the  end  of  an  item’s  useful  life  its  future  value  is  called  its  scrap  value.  

 There  are  3  methods  in  which  to  calculate  depreciation:  flat  rate  depreciation  (studied  here);  reducing  balance  depreciation  (studied  later)  and  unit  cost  depreciation  (studied  next)  

Flat  rate  (straight  line  depreciation)  If  an  item  depreciated  by  the  flat  rate  method,  then  the  value  decreases  by  a  fixed  amount  each  time  interval.  It  may  be  expressed  in  dollars  or  as  a  percentage  of  the  original  cost  price.  

As  the  depreciation  value  is  the  same  for  each  interval,  it  is  an  example  of  straight  line  decay.  This  relationship  can  be  expressed  in  the  following  recurrence  relation:  

 The  future  value  can  also  be  calculated  after  n  periods  of  depreciation.  

 We  can  use  the  above  relationships  or  a  depreciation  schedule  (table)  to  analyse  flat  rate  depreciation.  

Example  6.1  Fast  Word  Printing  Company  bought  a  new  printing  press  for  $15  000  and  chose  to  depreciate  it  by  the  flat  rate  method.  The  depreciation  was  15%  of  the  prime  cost  each  year  and  its  useful  life  was  5  years.  a)  Find  the  annual  depreciation.            b)  Set  up  a  recurrence  relation  to  represent  the  depreciation            

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c)  Complete  a  depreciation  schedule  for  the  useful  life  of  the  press  and  use  it  to  draw  a  graph  of  book  value  against  time.  

 

d)  Generate  the  relationship  between  the  book  value  and  time  and  use  it  to  find  the  scrap  value.              Example  6.1(c)  and  (d)  on  CAS  calculator

 

(c)  On  a  lists  &  spreadsheet  page  Label column A “n” and column B “Vn” Enter 0 to 5 in the n column and the starting value 15000 (V0) in cell b1.      In  cell  b2:  Enter  the  equation  “=b1-­‐2250”  This  equation  is  just  Vn+1=Vn-­‐2250  found  in  part  (b)  Note:  the  2250  is  the  annual  depreciation  found  in  part  (a)  

Press  enter,  then  fill down (b33) until n=5 Vn=3750  when  n=5.  So,  this  is  the  scrap  value

Add  a  Data  &  Statistics  page  Label  the  x-­‐axis  “n”  and  the  y-­‐axis  “Vn”  

 

In  this  worked  example  the  depreciation  schedule  gives  the  scrap  value,  when  n=5  Vn=$3750.  This  can  also  be  seen  in  the  graph  of  book  value  against  time,  since  it  is  only  drawn  for  the  item’s  useful  life  and  its  end-­‐point  is  the  scrap  value.  

Time  n  (yrs)  

Depreciation  d  ($)  

Future  value  Vn  ($)  

0      1      2      3      4      5      

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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Exercise  6  

1.   The  following  recurrence  relation  can  be  used  to  model  the  flat  rate  of  deprecation  of  a  set  of  office  furniture:  V0  =12000,  Vn+1  =Vn  +1200, where  Vn  is  the  value  of  the  furniture  after  n  years.    

a)   What  is  the  initial  value  of  the  furniture?  By  how  much  does  the  furniture  decrease  in  value  each  year?  

b)   Write  down  the  rule  for  the  value  of  the  furniture  after  n  years.  c)   Use  a  rule  to  find  the  value  of  the  investment  after  6  years.  

d)   How  long  does  it  take  for  the  furniture’s  value  to  decrease  to  zero?    e)   A  photocopier  in  the  office  costs  $6000  when  new.  Its  value  depreciates  at  the  flat  rate  of  17.5%  

of  its  new  value  each  year.  What  is  its  value  after  4  years?  2.     The  value  of  a  sewing  machine  after  n  years,  Vn,  can  be  calculated  from  the  rule:  

Vn  =  1700  −  212.5n.  

a)   By  how  much  is  the  value  of  the  sewing  machine  depreciated  each  year  in  dollars?    

b)   Usetheruletofindthevalueofthesewingmachineafter4years.    c)   The  sewing  machine  depreciates  by  12.5%  of  its  purchase  price  each  year.  Use  this  

information  to  determine  its  value  after  8  years.    3.     The  value  of  a  harvester  after  n  years,  Vn,  can  be  calculated  from  the  rule:  

Vn  =  65000  −  3250n.

a)   What  is  the  percentage  depreciation  for  the  harvester?  b)   Use  the  rule  to  find  the  value  of  the  harvester  after  7  years.  c)   How  long  does  it  take  the  harvester  to  reach  a  value  of  $29250?    

4.     A  computer  is  purchased  for  $5600  and  is  depreciated  at  a  flat  rate  of  22.5%  per  year.    

a)   Determine  the  annual  depreciation  in  dollars.  b)   Write  down  a  recurrence  relation  to  model  the  value  of  the  computer,  Vn,  from  year  to  year  

c)   Write  down  a  rule  for  the  value  of  the  computer,  Vn,  after  n  years.    

d)   Use  your  rule  in  part  c)  to  find:  i   the  value  of  the  computer  after  3  years   ii   the  number  of  years  it  takes  for  the  computer  to  be  worth  nothing.    

5.  A  machine  costs  $7000  new  and  depreciates  at  a  flat  rate  of  17.5%  per  annum.  The  machine  will  be  written  off  when  its  value  is  $875.    

a)   Write  down  a  recurrence  relation  to  model  the  value  of  the  machine,  Vn,  from  year  to  year  b)   Write  down  a  rule  for  the  value  of  the  machine,  Vn,  after  n  years.    c)   Use  your  rule  in  part  b)  to  find:  

i.   the  value  of  the  machine  after  2  years    ii     the  number  of  years  the  machine  will  be  used.    

   

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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7.  Unit-­‐cost  depreciation  The  unit  cost  method  is  based  upon  the  maximum  output  (units)  of  the  item.  For  example,  the  useful  life  of  a  truck  could  be  expressed  in  terms  of  the  distance  travelled  rather  than  number  of  years.  The  actual  depreciation  per  year  would  be  a  measure  of  the  number  of  kilometres  travelled.  

Unit  cost  depreciation  recurrence  relation  

The  future  value  over  time  using  unit  cost  depreciation  can  be  expressed  by  the  recurrence  relation:  

 

A  future  value  after  𝑛  outputs  using  unit  cost  depreciation  can  be  expressed  as:  

 

Example  7.1  

A  hairdryer  in  a  salon  was  purchased  for  $850.  The  value  of  the  hairdryer  depreciates  by  25  cents  for  every  hour  it  is  in  use.  Let  𝑉𝑛  be  the  value  of  the  hairdryer  after  𝑛  hours  of  use.    

a)   Write  down  a  rule  to  find  the  value  of  the  hairdryer  after  𝑛  hours  of  use.    

b)   What  is  the  value  of  the  hairdryer  after  50  hours  of  use?    

c)   On  average,  the  salon  will  use  the  hairdryer  for  17  hours  each  week.  How  many  weeks  will  it  take  the  value  of  the  hairdryer  to  halve?  

   

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Year  10  General  Maths  Unit  2     Topic  2  -­‐  Linear  Growth  and  Decay    

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Exercise  7  

1.    The  value  of  a  taxi  after  𝑛  kilometres,  𝑉𝑛,  can  be  calculated  from  the  rule:  𝑉𝑛 = 29000 − 0.25𝑛. a)   What  is  the  purchase  price  of  the  taxi?  

b)   By  how  much  is  the  value  of  the  taxi  depreciated  per  kilometre  of  travel?  

c)   What  is  the  value  of  the  taxi  after  20,000  kilometres  of  travel?  

d)   Find  how  many  kilometres  have  been  travelled  if  the  taxi  is  valued  at  $5000.      2.    A  car  is  valued  at  $35  400  at  the  start  of  the  year,  and  at  $25  700  at  the  end  of  that  year.  During  that  year,  the  car  travelled  25  000  kilometres.    

a)   Find  the  total  depreciation  of  the  car  in  that  year  in  dollars.    b)   Find  the  depreciation  per  kilometre  for  this  car.    

c)   Using  V0  =  25  700,  write  down  a  rule  for  the  value  of  the  car,  Vn,  after  n  kilometres.    

d)   How  many  kilometres  are  travelled  when  the  value  of  the  car  is  $6688?    

e)   Including  the  first  year  of  travel,  how  many  kilometres  in  total  is  this  car  expected  to  drive  before  it  has  a  value  of  zero?    

 3.    A  printing  machine  costing  $110  000  has  a  scrap  value  of  $2500  after  it  has  printed  4  million  pages.    

a)   Find:  i.     the  unit  cost  of  using  the  machine    

ii.     the  value  of  the  machine  after  printing  1.5  million  pages

iii.   the  annual  depreciation  of  the  machine  if  it  prints  750000  pages  per  year.    

b)   Find  the  value  of  the  machine  after  5  years  if  it  prints,  on  average,  750,000  pages  per  year.    

c)   How  many  pages  has  the  machine  printed  by  the  time  the  value  of  the  machine  is  $70  000?