Question

A bag contains 27 balls of which some are white and some are red. A ball is chosen at random. The probability of getting a red ball is $\frac{2}{3}$. Find the number of white balls.

Answer 1

Let the number of white balls in the bag be x.
Then, the number of red balls = ( 27 − x)
Given: P(red ball) = $\frac{2}{3}$
∴ $\frac{27-x}{27}=\frac{2}{3}\Rightarrow \frac{27-x}{9}=\frac{2}{1}\Rightarrow 27-x=18\Rightarrow x=27-18=9$
Hence, the number of white balls in the bag is 9.