1TH/Vwo §2.4 Decimal numbers

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Slide 1 - Diapositive

§ 2.4 Decimal numbers
Some important points follow now!

Slide 2 - Diapositive

Fractions  -  decimal numbers
These are closely linked together!
We can write a fraction as a decimal number:
= 0.8,   or 
                                                             = 0.75


54
43

Slide 3 - Diapositive

In order to write a fraction as a decimal number,
 we first have to write the fraction with a denominator of 10, 100 or even 1000!
For example:
5                =    5                 =  5.85                                 

             =               =                = 0.175   Now try yourself!
2017
407
10085
20035
1000175
10085

Slide 4 - Diapositive

306
Task 1: Write as a decimal number:

Slide 5 - Carte mentale

Task 1  Explanation:
We have to have a number like 10, 100 or 1000 as a denominator!

=                         =                   =   0.2        
306
51
102

Slide 6 - Diapositive

write as a decimal number:

2503
A
0.12
B
0.012
C
1.2
D
0.0012

Slide 7 - Quiz

Task 2  Explanation:
Now we even need to have 1000 as a denominator!
=                         =       0.012               
2503
100012

Slide 8 - Diapositive

Slide 9 - Diapositive

Rounding off can give us a better overview:
For example:
If you read in the papers that 
'298 785 sheep were transported,
it makes sense to round this off:
'About 300 thousand sheep were transported.'

Slide 10 - Diapositive

Rounding off ... (1)
see next slide how to do this!

Slide 11 - Diapositive

Rounding off ... (2)
Your marks are also rounded off to one decimal place at the end of the year:
+      7.79 for French become a 7.8 on your report
+      5.73 for History becomes a 5.7 on your report
How does this work? Let's have a closer look!

Slide 12 - Diapositive

round to two decimal places:
4.7386
A
4.73
B
5.74
C
4.74
D
473

Slide 13 - Quiz

Slide 14 - Diapositive

4.73 86
Rule for rounding off:
If the digit to the right of 3 is '5 or higher', then 3 is made one higher.
In this case: 8 is certainly '5 or higher', so the rounded number is:  4.74
So you see:   the 3 turns into a 4!

Slide 15 - Diapositive

4.7386    .......
becomes 4.74,
because the '8', after the '3', is higher than 4. 

Slide 16 - Diapositive

Task 3: Round to two decimal places:
79.6754

Slide 17 - Carte mentale

This is how it should've been done:
79.6754                      79.68
Because 5 is '4 or more',  the 7 is made one higher!

Slide 18 - Diapositive

Slide 19 - Diapositive

Slide 20 - Diapositive

round to three decimal places:
3.670587
A
3.670
B
3.671
C
3.67

Slide 21 - Quiz

Round to two decimal places:
93.098
A
94
B
93.09
C
93.10

Slide 22 - Quiz

Round to two decimal places:
 73.098
This one is a bit tricky!
Between the 9 and the 8 a dotted line is drawn.
Because the 8 is higher than a 4, the previous digit, 9, is
made one higher. So we write down '10', as follows:
73.10

Slide 23 - Diapositive

Homework time
+ now do §2.4 Decimal numbers
+ check your work with the Solutionsbook
+ good luck!   

Slide 24 - Diapositive