PROBABILITY 1

A number is chosen at random from 21 – 32 inclusive. Find the probability that it is a prime or a multiple of 3.

Solution

THIS IS A MUTUALLY EXCLUSIVE EVENT

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, 31, 32} = 12

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

n(R) = {23, 29, 31} = 3

P(M) = ⁴/12

P(R) = ³/12

………………………….

P(MuR) = P(M) + P(R)

P(MuR) = ⁴/12 + ³/12

              = ⁷/12

              = ⁷/12

P(MuR) = ⁷/12 answer

TRY THIS…………………

A number is chosen at random from 17 – 30 inclusive. Find the probability that it is a prime number or a multiple of 4.