1TH/Vwo §7.3 Decimal numbers

• Wiskunde
• Middelbare school
• havo, vwo
• Leerjaar 1

§7.3 Decimal numbers

You all know about decimal numbers.

It is similar to fractions, but now written with a point and not with a fraction symbol.

So:   0.5    instead of   

​2​​1​​

The same 'order of operations' as you learnt applies,

also with decimal numbers included!

8 - 4 x 1.5 =

1. 6
2. 18
3. -2
4. 2

explanation:

First comes X  and only then we do  -,  so:

8 - 4 x 1.5 =

8 - 6 = 2

0.01 x 2000 = ...

1. 200
2. 20
3. 200000
4. 20000

Realize that:

When the decimal point goes

- to the right, then the number gets greater, for example:

    10 x 0.03 = 0.3     or     100 x 0.003 = 0.03            or.    300 x 0.002 = 0.6

- to the left, then the number gets smaller, for example:

     0.01 x 240.8 = 2.408      or.  0.003 x 2222.2 = 6.6666

The next slide summarizes all this!

5.6 x 0.01 = ....

1. 5600
2. 0.56
3. 0.056
4. 560

explanation:

multiplying by 0.01 is the same as taking 

of that number, or placing the decimal point 2 places to the left, so:

5.6 x 0.01 = 0.056

 

​100​​1​​

Finally a remark about exercise 25:

In 25 the calculations have become that complicated, that it is important to work them out in a few steps!

Look at the following example.

This becomes pretty tricky, reason for us to work it out on paper like this:

0.1 x 14 x 100 =

 1.4 x 100 = 140

So first the brackets, then the square and finally the 2 multiplications!

When doing exercise 25 in a few minutes, make such calculations!!

One more TASK: a FOTOVRAAG!

      4.2 + (      - 28) =

+ Copy this task in your Notebook

+ write down the CALCULATION and only then the ANSWER

+ take a picture and 

+ send it in in the FOTOVRAAG!

8​2​​

VWO task
Send in a pic of your CALCULATION!

4.2+(8​2​​−28)=

Explanation:

4.2 + (      - 28)  =               Brackets first.

4.2 + (64 - 28) =               Between the brackets: the power first.

4.2 + 36  =   

40.2                        

8​2​​

Homework time

Do § 7.3 now.

However, don't forget to WORK OUT exercise 25, so don't 

only give the answers!