# 3TH / VWO §9.1/§9.4 Calculating with fractions

3T havo §9.1 Calculating with fractions
3T vwo §9.4  the same (almost)!
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Slide 1: Tekstslide
WiskundeMiddelbare schoolhavoLeerjaar 3

In deze les zitten 21 slides, met interactieve quizzen en tekstslides.

Lesduur is: 50 min

## Onderdelen in deze les

3T havo §9.1 Calculating with fractions
3T vwo §9.4  the same (almost)!

#### Slide 1 -Tekstslide

A short recap:
When adding or subtracting fractions, the denominators (noemers) have to be the same. If they're not, let's make them the same! As follows:

53+76=3521+3530=3551

#### Slide 2 -Tekstslide

+ Now with variables too!
+ Many times we just multiply the denominators to find the new one.
+ Like here: 5 x 8 = 40

#### Slide 3 -Tekstslide

+ another one comes up
+ watch: the 2nd fraction is not changed by us!
+ 5x is a fine denominator

#### Slide 4 -Tekstslide

+ One more.
+ The final result has a sum as numerator.
+ That's because 4 and 3x are not like terms!

#### Slide 6 -Tekstslide

Take a scrap paper (or your Notebook) and work out:
Write as one fraction and key in your answer in the next slide:

#### Slide 9 -Tekstslide

Do you remember that doing 'times' is much simpler than doing
'plus or minus', with fractions?
Reason: denominators may be unequal. Who cares?

x             =                    =
65
83
4815
165

#### Slide 10 -Tekstslide

I remember something about making denominators equal. So here I go about the job:

x                  =                                         x                    =

However now I am completely stranded.....         So let's look once more at the right way to do it!

65
83
4815
165
4818
4840
.....75
........

#### Slide 11 -Tekstslide

Do you remember that doing 'times' is much simpler than doing
'plus or minus', with fractions?
Reason: denominators may be unequal. Who cares?

x             =                    =
65
83
4815
165

#### Slide 12 -Tekstslide

When multiplying we just multiply numerators and
denominators. Period!

#### Slide 13 -Tekstslide

Simplification is the reverse of multiplication.
Now we divide numerator and denominator by the same number!

#### Slide 14 -Tekstslide

2 more examples of simplifications:
The book (where I took this from)
like to write the numbers as
products of letters and prime numbers
(priemgetallen). This may seem
unnecessary, but it makes clear
what is really happening when
simplifying!

#### Slide 15 -Tekstslide

Simplify yourself now and key in your answer in the next slide:

#### Slide 17 -Woordweb

The 2nd step
you may leave out.

#### Slide 19 -Tekstslide

There's one more new thing in §9.1....
That's about splitting up a fraction
in 2 new ones.
In exercises 8, 9 and 10 (havo)
and 32, 33 (vwo)
you'll discover
this for yourself!

Homework time