Question

A bag contains $5$ red balls and some blue balls. If the probability of drawing a blue ball is double that of red ball, find the number of blue balls in the bag.

Answer 1

Let Number of blue balls be $n$.

Now probability of getting of blue ball from bag equals to $n/n+5$ and probability of getting a red ball will be $5/n+5$.

From given condition , $n/n+5=2\ast 5/n+5$ which gives $n=10$