PROBABILITY 5

A number is chosen at random from 21 – 30 inclusive. Find the probability that it is a prime or a multiple of 4.

Solution

THIS IS A MUTUALLY EXCLUSIVE EVENT!

Let n(S) represent sample space

P(M) = probability of a multiple of 4

P(R) = probability of prime number

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

n(M) = {24, 28} = 2

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

P(M) = ²/10

P(R) = ²/10

………………………….

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

P(EuR) = ²/10 + ²/10

P(EuR) = ⁴/10 or ²/5 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.