# 1TH/vwo §8.4 Multiplying and division

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Slide 1: Slide
WiskundeMiddelbare schoolhavo, vwoLeerjaar 1

This lesson contains 37 slides, with interactive quizzes and text slides.

Lesson duration is: 30 min

## Items in this lesson

§8.4

#### Slide 2 -Slide

It is good to realise that x  and  :  are each others reverse!
For example:
48 : 8 = 6,  because 6 x 8 = 48 !
In this LessonUp you will get
+ new Information and
+ also quite a few short Tasks,
to Practise this new Information.

#### Slide 3 -Slide

funny witch - strange brews ...
Remember the witch? From all the strange brews.
Once upon a day she wants to work quicker
with her cold and hot blocks.
She wants to put in or take out MORE temperature blocks
IN ONE GO! For this she uses a BUCKET.
This is what this § is about.

#### Slide 6 -Slide

Adding a bucket of 6 cold blocks
4 times makes the temperature in the cauldron ...
timer
0:20
A
rise
B
fall
C
stay the same

#### Slide 7 -Quiz

Adding COLD BLOCKS make the temperature FALL.
NEW QUESTION: By how many degrees does it fall?
Remember: she adds 6 cold blocks 4 times!

#### Slide 8 -Slide

Adding 6 cold blocks 4 times make the temperature fall by ... degrees.
timer
0:30
A
24
B
-24
C
6
D
-6

#### Slide 9 -Quiz

SOLUTION:
The temperature gets lower, of course!
However, it falls by 24 degrees and not by -24 degrees.
In other words: is gets colder by 24 degrees.

#### Slide 10 -Slide

Answer in the next slide again.

#### Slide 11 -Slide

What happens to the temperature if 3 Cold Blocks are REMOVED 5 times?
timer
0:25
A
it falls by 3 degrees
B
it rises by 3 degrees
C
it falls by 15 degrees
D
it rises by 15 degrees

#### Slide 12 -Quiz

Solution:
This is a bit tricky!
Removing cold blocks makes it LESS COLD  in the kettle.
So it gets 5 x 3 = 15 degrees WARMER!

#### Slide 13 -Slide

answer c, below, in the next slide.

#### Slide 14 -Slide

timer
0:30
removing a bucket of 3 cold blocks 5 times
gives this calculation:

#### Slide 15 -Mind map

- 5 x -3 = 15                           So: minus times minus is positive.                                              or:                                                    -            x            -        =      +
' -3 '   means 3 COLD Blocks and
'-5'      means 5 buckets are REMOVED from the cauldron.

A
50-55
B
55-60
C
60-65
D
65-70

#### Slide 18 -Quiz

Question : What mistake was made in the 2nd line? ('removed 6 times .......')

#### Slide 19 -Slide

The mistake in the second line is:
-6 x 8 = ....    this wrong, as it read that there were 8 COLD blocks!
-6 x -8 = 48     is what it should've been!
Now a little joke.

#### Slide 21 -Slide

The funny part is this:
To have been around the block means also:
to have a lot of experience with something!

#### Slide 22 -Slide

Let's discuss this table.
First ALL THINK ABOUT the 1st line. Then ONE GETS THE TURN to explain it.
Then we do the same with the 2nd line, etcetera.

#### Slide 23 -Slide

Above you see the Basic Rules for Multiplying with
Positive and Negative Numbers.
Realise that you can always relate all these Calculations
to:     Hot and Cold Blocks in a number of Buckets, that are added or removed from the kettle!

#### Slide 24 -Slide

The reverse of multiplying is ....
dividing!

#### Slide 26 -Slide

24 : -8 = -3, because ....
(make the multiplication!)
timer
0:20
A
3 x -8 = -24
B
-3 x 8 = -24
C
-3 x -8 = 24
D
3 x 8 = 24

#### Slide 27 -Quiz

Solution:
-3 x -8 = 24

#### Slide 28 -Slide

In this way, we can make Basic Rules for all 4 types of
divisions (=delingen) with positive and negative numbers!
See next slide.

#### Slide 30 -Slide

In short we write it as follows:
+    :    + =    +
+   :     -   =   -
-    :    +   =   -
-    :   -    =   +

#### Slide 32 -Slide

-18 : -9 = ......
because ..... x ..... = .....

The Numbers to be filled in are:
timer
0:45
A
-2, -2, 9, 18
B
-2, -2, -9, -18
C
2, -2, -9, 18
D
2, 2, -9, -18

#### Slide 33 -Quiz

SOLUTION:
We just learned that:
a negative number divided by a negative number is a positive number.
So            - 18 : -9 = 2, because 2 x -9 = -18  !

#### Slide 34 -Slide

Homework:

HV1Y:      §8.4.   not 25 and 26

#### Slide 35 -Slide

Homework:

HV1Y:                             30 t/m 35 S 30 and S32, p.63
G1X, A1X and C1X:    30 t/m 35 also do C7 +  C8,  p.63

#### Slide 36 -Slide

That's all, folks!