Question

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

Answer 1

let number of blue balls = $n$

$\therefore$ total balls = $(n+5)$

P(blue ball) = $\frac{n}{n+5}$

P(red ball) = $\frac{5}{n+5}$

as per question,

P(blue ball) = 3 $\times$ P(red ball)

$\frac{n}{n+5}$ = $3\times \frac{5}{n+5}$

$\therefore n=15$