# CAT Practice : Averages, Ratios, Mixtures

When we mix two mixtures in a particular ratio, we get a third mixture. Given the third mixture how does one find the ratio in which they were mixed.

## Change in average

Q.20: In class A, the ratio of boys to girls is 2 : 3. In class B the ratio of boys to girls is 4 : 5. If the ratio of boys to girls in both classes put together is 3 : 4, what is the ratio of number of girls in class A to number of girls in class B?

3 / 5

## Detailed Solution

Let us assume class A has 2x boys and 3x girls, class B has 4y boys and 5y girls.

2x + 4y / 3x + 5y
=
3 / 4

8x + 16y = 9x + 15y
x = y

Required ratio =
3x / 5y
(since x = y) =
3 / 5

3 / 5

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