# 1718 WB1Z CH4+8 Lesson 8

What exercises should I discuss on the board?
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Slide 1: Mind map
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This lesson contains 25 slides, with interactive quizzes and text slides.

Lesson duration is: 50 min

## Items in this lesson

What exercises should I discuss on the board?

#### Slide 1 -Mind map

5 + 2 = 7                                                   5 + - 2 = 3

Subtracting a positive number     Subtracting a negative number
5 - 2 = 3                                                     5 - - 2 = 7

#### Slide 2 -Slide

Multiplication
You can also multiply with negative numbers. A good way to think about multiplication is to think of a bucket.

You can add or subtract several buckets of hot or cold blocks to change the temperature.

#### Slide 3 -Slide

Multiplication
If you add 5 buckets with 3 hot blocks in each bucket, how does the temperature change?

3
3
3
3
3

#### Slide 4 -Slide

If you add 5 buckets with 3 hot blocks in each bucket, how does the temperature change?

#### Slide 5 -Mind map

Multiplication
If you add 5 buckets with 3 hot blocks in each bucket, how does the temperature change?

5 x 3 = 15
The temperature rises by 15 degrees
3
3
3
3
3

#### Slide 6 -Slide

Multiplication
If you add 4 buckets with 5 cold blocks in each bucket, how does the temperature change?

5
5
5
5

#### Slide 7 -Slide

If you add 4 buckets with 5 cold blocks in each bucket, how does the temperature change?

#### Slide 8 -Mind map

Multiplication
If you add 4 buckets with 5 cold blocks in each bucket, how does the temperature change?

4 x - 5 = -20
The temperature falls by 20 degrees.
5
5
5
5

#### Slide 9 -Slide

Multiplication
If you remove 5 buckets with 8 hot blocks in each bucket, how does the temperature change?

8
8
8
8
8

#### Slide 10 -Slide

If you remove 5 buckets with 8 hot blocks in each bucket, how does the temperature change?

#### Slide 11 -Mind map

Multiplication
If you remove 5 buckets with 8 hot blocks in each bucket, how does the temperature change?

- 5 x 8 = -40
The temperature falls by 40 degrees
8
8
8
8
8

#### Slide 12 -Slide

Multiplication
If you remove 3 buckets with 6 cold blocks in each bucket, how does the temperature change?

6
6
6

#### Slide 13 -Slide

If you remove 3 buckets with 6 cold blocks in each bucket, how does the temperature change?

#### Slide 14 -Mind map

Multiplication
If you remove 3 buckets with 6 cold blocks in each bucket, how does the temperature change?

- 3 x - 6 = 18
The temperature rises by 18 degrees
6
6
6

#### Slide 15 -Slide

Rules for multiplication
positive x positive = positive                 5 x 3 = 15
positive x negative = negative              4 x -5 = -20
negative x positive = negative              -5 x 8 = -40
negative x negative = positive              -3 x -6 = 18

-3 x 7 =

-6 x -5 =

#### Slide 18 -Open question

Division

Division is the inverse of multiplication.
We can use this to find the rules for division.

Division

#### Slide 20 -Slide

Rules for division

28 : -4 =

#### Slide 22 -Open question

Rules for multiplication & division

#### Slide 23 -Slide

Powers
When working with powers and negative numbers, remember the rules for opposite numbers:

#### Slide 24 -Slide

Homework
§8.4: make and correct 25 - 36