PROBABILITY C3

A number is chosen at random from 21 – 30 inclusive. Find the probability that it is a prime or a multiple of 3.

Solution

Let n(S) represent sample space

P(M) = probability of a multiple of 3

P(R) = probability of prime number

n(S) = {21, 22, 23, 24, 25, 26, 27, 28, 29, 30} = 10

n(M) = {21, 24, 27, 30} = 4

n(R) = {23, 29} = 2

P(M) = ⁴/10

P(R) = ²/10

………………………….

P(EuR) = P(E) + P(R)

P(EuR) = ⁴/10 + ²/10

P(EuR) = ⁶/10 or ³/5 answer

TRY THIS…………………

A number is chosen at random from 21 – 35 inclusive. Find the probability that it is a prime or a multiple of 7.