# Math Help - Dividing ratios.

1. ## Dividing ratios.

A question has come up on a mock exam and i'm not sure if i have done it correctly so please can you tell me if i have done it wrong or if it is right?

Peter and Margaret's ages are in the ratio 4:5. If Peter is 16 years old, how old is Margaret?

Peter = 4/9
so 1/9 is 16 divided by 4 = 4
4 x 5 = 20
Margaret is 20.

2. you have the right answer

3. Originally Posted by mollyx
A question has come up on a mock exam and i'm not sure if i have done it correctly so please can you tell me if i have done it wrong or if it is right?

Peter and Margaret's ages are in the ratio 4:5. If Peter is 16 years old, how old is Margaret?

Peter = 4/9
so 1/9 is 16 divided by 4 = 4
4 x 5 = 20
Margaret is 20.

Correct, but there is an easier approach.

The question is essentially saying:

$4:5=16:?$

And, as you know that 4 x 4 = 16
To find out the missing value, just do the same thing to the other side of the ratio:
5 x 4 = 20