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

Suppose number of black ball = x

It is given that White balls = 15

According to question,

P(Black balls) = 3 × P(White balls)

`=> x/(15+x) = 3 xx 15/(15 + x)`

`=> x = 45`

Hence, number of black ball are 45.