Question

A box contains $20$ balls bearing numbers, $1,2,3,4,.....20$. A ball is drawn at random from the box. What is the probability that the number on the ball is prime number

• A. $\frac{1}{5}$
• B. $\frac{2}{5}$
• C. $\frac{3}{5}$
• D. $\frac{4}{5}$

Answer 1

The correct option is B $\frac{2}{5}$

Here, totat numbers are $20$.
$\therefore$ Total number of elementary events =$20$
There are 8 prime number from $1$ to $20$, ie , $2,3,5,7,11,13,17,19$
$\therefore$ Favourable number of elementary events = $8$
P (Prime number)= $\frac{8}{20}=\frac{2}{5}$