# 1TH/vwo §8.3 Subtracting negative numbers

QUESTION FOR YOU:

WHAT IS THE KEY WORD IN THE LAST SENTENCE ?
In other words: what's NEW ?
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Slide 1: Tekstslide
WiskundeMiddelbare schoolhavo, vwoLeerjaar 1

In deze les zitten 33 slides, met interactieve quizzen en tekstslides.

Lesduur is: 30 min

## Onderdelen in deze les

QUESTION FOR YOU:

WHAT IS THE KEY WORD IN THE LAST SENTENCE ?
In other words: what's NEW ?

#### Slide 2 -Tekstslide

THE KEY WORD IS .....

#### Slide 3 -Woordweb

SOLUTION:
THE KEY WORD IS:       REMOVING!
In §9.2 the witch only ADDED hot and cold blocks,
but in §9.3 she TAKES OUT hot and cold blocks!

#### Slide 6 -Tekstslide

Let's PRACTICE this some times.
+ first your teacher gives an example,
+ then you get a little time to think about the next one
+ finally one of you gets the turn to speak up
+ SAFETY WARNING: taking out blocks is more difficult than putting in!

#### Slide 8 -Tekstslide

In the same way we tackle 19 now.
+ now however a CALCULATION is asked, too
+ for example:
6 - -5 = ...          A double minus?! Yes! The first minus is from 'TAKING OUT'
and the second minus is from a COLD BLOCK. Let's just practice this!
+ give it your best shot!

Which whitch?

#### Slide 13 -Tekstslide

So we get this:
1 - 4 = -3

#### Slide 15 -Tekstslide

In fact        --        can be written as          +            !
So we get this:
5 -- 2 = 5 + 2 = 7

5 - ..... = -3
timer
0:20
A
-8
B
2
C
8
D
-2

#### Slide 17 -Quizvraag

5 -   .... = -3
Start number is  5
The result is  -3
So we subtract 8.  That's the number that has to be filled in on the dots!
In whitches' words: The temperature in the kettle is 5 degrees.
To get -3 as new temperature she TAKES OUT 8 HOT BLOCKS.
ATTENTION: the next task isn't as easy as it may look!

timer
1:00

#### Slide 20 -Woordweb

With arrows (=pijlen) on a number line once more!
We have to cover the distance from 2      to      -3
That distance is 5
However, we move TO THE LEFT on the number line and that means subtracting!
So the answer is:    5           Do you see how tricky this business is?!
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#### Slide 21 -Tekstslide

Once more, we move TO THE LEFT on the number line and that means subtracting!
The complete calculation becomes:
2       -    5          =     -3

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#### Slide 22 -Tekstslide

This is called rear ending a car.
This also happens to witches.

#### Slide 24 -Tekstslide

Find the outcome for this task.
Someone will get the turn.

timer
0:05

#### Slide 25 -Tekstslide

Find the outcome for second task.
Someone will get the turn.

timer
0:23

#### Slide 26 -Tekstslide

Find the outcome for third task.

timer
0:30

My outcome is:

Solutions:

#### Slide 30 -Tekstslide

8.5 + ... = - 2.5
timer
0:40
A
11
B
-10
C
-11
D
-6

#### Slide 31 -Quizvraag

Going from +8.5  to  -2.5  means going 8.5 + 2.5 to the left.
So:
8.5  +  -11  =  -2.5                 '-11'  has to be filled in.

#### Slide 32 -Tekstslide

Homework time
Now do §8.3
T vwo, do:         21  t/m 24 and  C5 + C6
As you are nearing the end of the 1st form,
doing the Challenge tasks becomes a usual thing!