Question

A bag contains 15 white and some black balls. If the probability of drawing a black ball from the bag is thrice that of drawing a white ball, find the number of black balls in the bag.

Answer 1

Given, no. of white balls = 15

Let no. of black balls = x

$\therefore$ Total balls = ( 15 + x )

According to the question,

P(Black ball) = 3 $\times$ P (White ball)

$\Rightarrow \frac{x}{(15+x)}=3\times \frac{15}{(15+x)}$

$\Rightarrow x=45$

$\therefore$ No. of black balls in bag = 45