Hello, jai!

A bag contains tennis balls:

of the balls are yellow, the other balls are white

John will take at random a ball from the bag.

He will note its colour and then put it back in the bag.

Then Mary will take at random a ball from the bag.

She will note its colour.

Given the probability than John and Mary will take balls with different colours is ,

. . prove that: .

We are told that this probability is

Hence: .

Divide by 2: .