Confidential 1

Multiplying Integers

Confidential 2

WARM-UP:

1.) 5 - 9 = -4

2.) 16 - (-20) = 36

3.) (-22) - 40 = -66

4.) (-65) - (-81) = 16

Confidential 3

Let's review what we learned in the last lesson.

Confidential 4

Confidential 5

Confidential 6

We are very familiar with Addition and it is easy for us to add

4 + 4 + 4 = 12

We can also think of this as three groups of 4 OR

3 x 4 = 12

Let's Get Started!

Confidential 7

0 4 8 12

On a number line, this might look like......

1 2 3

3 x 4 = 12

Confidential 8

So, let's look at

(-4) + (-4) + (-4) = -12

We know from our Addition Rules that when we add NEGATIVE numbers together, our sum is NEGATIVE.

We can also look at this as three groups of (-4) OR

3 x (-4) = -12

Confidential 9

On a number line, this might look like......

3 x (-4) = (-12)

40-4-8-12

123

Confidential 10

But what happens when we multiply a NEGATIVE number by a NEGATIVE number??????

Multiplying by a NEGATIVE number is the opposite of multiplying by a POSITIVE number so our products have opposite signs.

If 3 x (-4) = -12

Then (-3) x (-4) = +12

Remember that a "product" is the answer to a multiplication problem.

Confidential 11

Rules for Multiplying Integers

The product of two integers with the SAME sign is always POSITIVE.

The product of two integers with DIFFERENT signs is always NEGATIVE.

6 x 7 = +42

(-5) x (-4) = +20

8 x (-4) = -32

(-9) x 3 = -27

Confidential 12

Let's try a few!

Remember:SAME SIGNS PositiveDIFFERENT SIGNS Negative

1.) -6 x 4 = -24

2.) 10 x -5 = -50

3.) (-8) x (-9) = 72

4.) 7 x 6 = 42

5.) -11 x 8 = -88

Confidential 13

When we multiply 3 or more numbers together, ......

(-4) x 5 x (-2) =

...we begin by multiplying 2 at a time and inserting the appropriate sign.

(-20) x (-2)

+40

(-4) x 5 x (-2) = +40

Confidential 14

You try some.

6 x (-10) x (-2) = 120

(-5) x 7 x 2 = -70

Confidential 15

Good! Now let's work with multi-digit numbers.

-47 x 583 =

5 8 3larger number of digits goes on top

4 7x

1

2

8

5

4 0

1

23

3

2 3 x

10

1

472 ,-

Let's review.

Multiply first and then add the appropriate sign. Also, remember your comma!

multiply from right to left

Confidential 16

You try this one!

(-62) x (-941) =

larger number of digits goes on top

Be sure to add your COMMA and the appropriate sign.

2

9 4 1 X 6 2------------ 1 1

1 8 8 25 6 4 6 X------------5 8,3 4 2

Confidential 17

BREAK

Copyright © Ed2Net Learning, Inc.

18

GAME TIME !

Click here to play a game

Confidential 19

1.) Nancy lives 32 miles from her work. Howmany miles does she drive to and from workin a month? (Assume that a month has 4 weeksand Nancy works Monday through Friday.)

Total miles in a day 2 X 32 = 64 (to and fro)Total number of days in a month 5 X 4 = 20

so total miles in 20 days = 64 X 20 = 1280 miles

Confidential 20

2.) Erica baked chocolate chip cookies and broughtthem to her girl scout meeting. The girls ate halfthe cookies and the troop leaders ate 5 cookies. Erica took 15 cookies home with her after themeeting. How many cookies did she take to the

meeting?

Erica baked 40 cookies The girls ate 20 cookies (Half of what she

got.) Troop leader ate 5 so she is left with 15.

40 -20 – 5 = 15

Confidential 21

3.) Susie has $232 in her bank account. Shemakes 3 withdrawals of $85 each. How muchmoney must she deposit back into the account

inorder to have a balance of $25?

Total money $232Withdrew $85 X 3 = 255.Balance = 232 – 255 = (-23)To get balance of $25 she needs to deposit25 – (-23) = $48

Confidential 22

Let's see how well you understood the lesson today!

1.) (-8) x 12 = -96

2.) (-6) x (-20) = 120

3.) 2 x (-5) x 4 = -40

4.) (-7) x (-3) x (-1) = -21

5.) 3 x (-3) x 2 x (-2) = 36

6.) 32 x (-4) = -128

Confidential 23

7.)

2,903 x (-31) =

2

2, 9 0 3 X 3 1 --------------- 2 9 0 3 8 7 0 9 X-------------- 8, 9 9 9 3

Confidential 24

Let's review what we learned today!

Confidential 25

Confidential 26

Multiplying multi-digit numbers: 583 x (-47) =

Confidential 27

Great Job Today!

Remember to practice what you learned!