Question

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

• A. 2
• B. 4
• C. 8
• D. 6

Answer 1

The correct option is D 6

Given Number of white balls $=4

Let Number of red balls $=N$

then total balls $=N+4$

Probability of drawing a white ball from the bag would be

$P\left(whiteball\right)=\frac{Numberofwhiteballs}{Totalballs}=\frac{n\left(white\right)}{n\left(Total\right)}=\frac{4}{N+4}$

But Given $P\left(whiteball\right)=\frac{2}{5}$

So $P\left(whiteball\right)=\frac{2}{5}=\frac{4}{N+4}\frac{2}{5}=\frac{4}{N+4}2(N+4)=5\ast 42N+8=202N=20-8=12N=6$

So the number of red balls in the bag is $6$ red balls.