Question

A bag contains 4 white balls and some red balls. If the probability of drawing a white ball from the bag is $\frac{2}{5}$, find the number of red balls in the bag.

Answer 1

No. of white balls=4

Let number of red balls =x

Probability of drawn white ball, P(A) =$\frac{m}{n}\Rightarrow \frac{2}{5}=\frac{4}{x+4}$

By cross multiplication

2x+8=20$\Rightarrow 2x=20-8$

2x=12$\Rightarrow x=\frac{12}{6}=6$

$\therefore$ No. of red balls=6