1TH/Vwo §7.5 multiplying fractions

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

§7.5 Multiplying fractions

After   +       and        -     we now look at

the operation:       x   !

First we multiply a fraction by a whole number:

Now it's your turn:

​3​​2​​

x 33 = ...

solution:

another one for you:

3/13 x 52 = ....

1. 10
2. 9
3. 14
4. 12

Solution:

Now let's talk business:

Finally it's

Fraction times Fraction ...

What is the BEST answer to:

x = ...

​3​​2​​

​2​​1​​

1. 12/36
2. 1/3
3. 2/6

x                      =          =              

So when MULTIPLYING FRACTIONS you just do:

numerator x numerator,     divided by

denominator x denominator  !                         

​3​​2​​

​2​​1​​

​6​​2​​

​3​​1​​

WARNING:

How NOT to MULTIPLY FRACTIONS

watch next slide!

Mutiplying fractions in the wrong way:

 COMMON MISUNDERSTANDING; somebody tries to tackle the task below :

 Working with the common denominator: then the new denominator is 14 x 4

              

                x            =         x          =                          x                         ???

​14​​13​​

​4​​3​​

​56​​52​​

​56​​42​​

​.......​​......​​

​........​​.......​​

SOLUTION:

  When MULTIPLYING fractions with unequal denominators,

    you DON'T have to make them equal!!

Watch the next slides that show how simple it really is!

your turn again,

ANS

3/8 x 3/8 = ...

1. 9/8
2. 9/64
3. 6/16
4. 3/64

Solution:

Fotovraag: first COPY it and work it out in your Notebook, take a pic and send in in next slide!

 Show your CALCULATION!

Don't forget to SIMPLIFY your answer, in the end!

2/7 + 1/7 x 1/2 = ......

Solution:

Now it's time for a complicated one:

Tasks:

1. Copy this exercise in your Notebook.

2. Make this exercise.

3. Send in your answer in the next slide.

My answer is:

This is the Solution:

NOTE:

In the final answer you may also give as ONE FRACTION.

So:                 is a good answer, too!

​16​​19​​

!

Let's look at the next slide to see what could go wrong!

8 

 You might think:

2  x  3 = 6      and                 x          = 

So the final answer is:        6   +        =   6                 However this is WRONG!

What has been FORGOTTEN here is this:  2 x       and           x 3   !

​2​​1​​

​4​​1​​

​8​​1​​

​8​​1​​

​8​​1​​

​4​​1​​

​2​​1​​

​8​​1​​

Let's look at the next slide to see what could go wrong!

FOTOVRAAG:

again COPY it and work it out in your Notebook first and then send it in by a PICTURE:

1 1/8 x 1 1/3 = ......

Solution:

NOTE:

also          is a perfectly GOOD ANSWER !

​2​​3​​

Homework -sending in in GC again!-      :

§7.5 Make the tasks.

Do 36 e t/m h   (not a t/m d)     and

Do 37  d,e,f    (not a,b,c)

Skip: 38

- Make it

- Correct it with the Solutionsbook

- Take a few pictures and send them in in GC!