Question

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

Answer 1

Let there be $x$ blue balls.

So, the total number of balls $=x+5$

P(Blue ball) $=\frac{x}{(x+5)}$

P(Red ball) $=\frac{5}{(x+5)}$

Given,

P(Blue) $=2\times$ P(Red)

$\frac{x}{(x+5)}=2\times \frac{5}{(x+5)}$

Solving, we get $x$ as $10.$

So, the number of blue balls $=10.$