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?

Answer 1

Given: A box contains balls numbered 1, 2, ..., 20 and one ball is drawn at random.

Step-wise calculation:

1. Total number of equally likely outcomes = 20.

2. List the prime numbers between 1 and 20: 2, 3, 5, 7, 11, 13, 17, 19.

Number of favourable outcomes = 8.

3. Probability = `"Number of favourable outcomes"/"Total number of outcomes"`

4. Probability = `8/20`

= `2/5`

= 0.4

= 40%

The probability that the number on the drawn ball is prime is `2/5` (40%).