Post on 23-Feb-2016
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Math 8
Unit 3: Operations with Fractions
Unit 3: Operations with Fractions
What you’ll learn• Estimate the products and quotients of
fractions and mixed numbers• Multiply a fraction by a whole number and by
a fraction• Divide a fraction by a whole number and by a
fraction• Multiply and divide mixed numbers• Use the order of operations with fractions
Unit 3: Operations with Fractions
Why it’s important:• Used with cooking for measuring• Used with shopping (sales ½ off)• Used with construction for measuring
ReviewFractions are used to show parts of a
whole.
Fraction Review
41
Three parts out of four are coloured in.4
3
One part out of four is white.
Fraction Review
Review• The top is called the numerator.• The bottom is called the denominator.• The line is called the fraction bar.
41 numerator
denominator
fraction bar
Fraction ReviewReviewImproper fractions have a numerator larger than the denominator.Mixed fractions are a combination of whole number and fraction.
45 Improper
fraction411 Mixed
fraction
Fraction Review
ReviewEquivalent fractions – have the same value, they are multiples of each other.
41
82
Fraction Review
ReviewFind the smallest equivalent fraction.A. B.
C. D.
42
93
62
1812
• Equivalent fraction animation
Fraction ReviewReviewTo add or subtract fractions they must have the same denominator. Use equivalent fractions to get the same denominator.
41
82
Fraction Review
Make equivalent fractions by doubling the quarter.
The denominator must be the same for both fractions.
Reduce the fraction to the smallest possible equivalent fraction.
2184
82282
82
41
82
Fraction Review
Make equivalent fractions by halving the two eighths.
The denominator must be the same for both fractions.
Reduce the fraction to the smallest possible equivalent fraction.
2142
41141
41
41
82
3.1 USING MODELS TO MULTIPLY FRACTIONS AND WHOLE NUMBERS
Unit 3: Operations with Fractions
3.1 Using Models To Multiply Fractions and Whole Numbers
• Focus: Use models to multiply a fraction by a whole number
3.1 Using Models To Multiply Fractions and Whole Numbers
• To add fraction you must have the same denominator.
38
14+ =
3.1 Using Models To Multiply Fractions and Whole Numbers
• We change the second fraction into eighths.
38
28+ =
3.1 Using Models To Multiply Fractions and Whole Numbers
• We add the numerators.
38
28+ = 3+2
8 = 58
3.1 Using Models To Multiply Fractions and Whole Numbers
• Try:
31
31
21
61
41
31
3.1 Using Models To Multiply Fractions and Whole Numbers
Remember• Multiplication is accelerated addition• 2 + 2 + 2 = 6
• This can also be done as three groups of two
23
2 x 3 = 6
3.1 Using Models To Multiply Fractions and Whole Numbers
• Match the addition and multiplication
a. 3 + 3 + 3 + 3b. 5 + 5c. 2 + 2 + 2 + 2 + 2d. 1 + 1 + 1
•4 x 3•1 x 3•2 x 5•5 x 2
• Remember
155
3.1 Using Models To Multiply Fractions and Whole Numbers
• What is 3 times two thirds?
32
32
32
323
3.1 Using Models To Multiply Fractions and Whole Numbers
• What is 3 times two thirds?
236
32
32
32
236
32
13
323
3.1 Using Models To Multiply Fractions and Whole Numbers
• Write out the following multiplications as additions and draw a diagram.
322 c.
433 b.
214 a.
3.1 Using Models To Multiply Fractions and Whole Numbers
• Homework
3.2 USING MODELS TO MULTIPLY FRACTIONS
Unit 3: Operations with Fractions
3.2 Using Models to Multiply Fractions
• Focus: Use models to multiply fractions
3.3 MULTIPLYING FRACTIONSUnit 3: Operations with Fractions
3.3 Multiplying Fractions
• Focus: Develop an algorithm to multiply fractions
3.3 Multiplying Fractions
• We have seen how to multiply fractions by whole numbers.
1865
3.3 Multiplying Fractions
• Multiply the 5 by 18
1865
6185
690
15
• Reduce by dividing the numerator and denominator by 6
Method 1 - reduce at end
3.3 Multiplying Fractions
• Reduce by dividing 18 and 6 by 6. You must do the same to a numerator and denominator.
1865
118
65
15
• Multiply the numerators, then the denominators.
Method 2 - reduce at start
3
1
3.3 Multiplying Fractions
• Example
21
32
3.3 Multiplying Fractions
• Example
21
32
21
32
1
1
31
Split the coloured sections into two parts.
Keep one of the two parts.
210
56
3.3 Multiplying Fractions
• Example
210
56
2
1
Divide 5 out of 10 in the numerator and out of 5 in the denominator.Divide 2 out of 6 (or 2) in the numerator and out of 2 in the denominator.
1
3
6 16 or
3.4 MULTIPLYING MIXED NUMBERSUnit 3: Operations with Fractions
3.4 Multiplying Mixed Numbers
• Focus: Apply knowledge of multiplying fractions to multiply mixed numbers
3.4 Multiplying Mixed Numbers
To multiply mixed fractions, change the fraction into an improper fraction.
45 Improper
fraction411 Mixed
fraction
Remember:
3.4 Multiplying Mixed Numbers
• To change from mixed to improper:
newnumerator
wholenumber
denominator + numerator= x412
49
4142
3.4 Multiplying Mixed Numbers
• Convert to improper fractions:
321
412
543
412
3.4 Multiplying Mixed Numbers
• To convert to mixed fractions subtract the denominator from the numerator.
25
212
231
3.4 Multiplying Mixed Numbers
25
3.4 Multiplying Mixed Numbers
25
231
3.4 Multiplying Mixed Numbers
25
212
3.5 DIVIDING WHOLE NUMBERS AND FRACTIONS
Unit 3: Operations with Fractions
3.5 Dividing Whole Numbers and Fractions
• Focus: Use models to divide proper fractions and whole numbers
Remember:• Division is determining how many groups you
can make out of a tot
How many groups of 3 can you make out of 15?315
Remember:• Division is determining how many groups you
can make out of a total
How many groups of 3 can you make out of 15?315
5 groups
How many halves are in 1?
211
Try the following:
212
213
214
Try the following:
212
213
214
Is there a pattern? What is it?
Try
311
312
313
Is there a pattern? What is it?
Try
322
324
326
Try
322
324
326
• A “flipped” fraction is called an inverse or a reciprocal.
sreciprocal are 23 and
32
34 of inverse theis
43
Reciprocals are two numbers that multiply to produce 1.
sreciprocal are 23 and
32
1
23
32
23
32
1 1
1 1
• To divide fractions, invert the second fraction and multiply.
23
52
32
52
35
21
53
21
TryA. B. C.
51
54
31
65
51
313
3.6 DIVIDING FRACTIONSUnit 3: Operations with Fractions
3.6 Dividing Fractions
• Focus: Develop algorithms to divide fractions.
3.7 DIVIDING MIXED NUMBERSUnit 3: Operations with Fractions
3.7 Dividing Mixed Numbers
• Focus: apply knowledge of dividing fractions to divide mixed numbers
3.8 SOLVING PROBLEMS WITH FRACTIONS
Unit 3: Operations with Fractions
3.8 Solving Problems with Fractions
• Focus: Identify the operation required to solve a problem involving fractions
3.8 Solving Problems with Fractions
• A pancake recipe makes enough pancakes for 12 people. Sally has to make enough pancakes for 7 people. The recipe needs 10 cups of pancake mix. How much pancake mix should Sally use?
3.8 Solving Problems with Fractions
• The student’s spirit group does a survey. 2/3 of the students want a Christmas dance. If 150 students were surveyed, how many do not want a dance?
3.8 Solving Problems with Fractions
• A sports store examines its receipts. 3/5 of the clothing sold was men’s wear. If the store has 9 000 ft2 of clothing area, how much area should be men’s wear?
3.8 Solving Problems with Fractions
• For a wedding reception 3/5 of the meals are beef, 1/3 of the meals are chicken, while the rest were vegetarian.
a. What fraction of the meals are vegetarian?b. If there are 90 guests, how many people
ordered beef?
3.9 ORDER OF OPERATIONS WITH FRACTIONS
Unit 3: Operations with Fractions
3.9 Order of Operations with Fractions
• Focus: Use the order of operations to evaluate expressions
3.9 Order of Operations with Fractions
Remember• Order of operations:BracketsExponentsDivisionMultiplicationAdditionSubtraction
}} Done at the same time from
left to right
Done at the same time from left to right
3.9 Order of Operations with Fractions
• Try
51
54
12
51
58
59
Multiply first
Add second
3.9 Order of Operations with Fractions
• Try
56
13
34
Divide first, invert second fraction and multiply
65
13
34
Simplify and multiply1
2
25
34
615
68
623
Add
Reduce
3.9 Order of Operations with Fractions• Try
61
31
21 There is a hidden multiply between
the ½ and bracket. Add first by finding a common denominator.
61
62
21
Add in the brackets
21
21
63
21
41
Reduce 3/6 and get rid of brackets
Multiply fractions