A number is selected at random from the first 40 natural numbers. What is the probability that the number is a multiple of either 2 or 21?
Answers.
A) 21 / 40  B) 2 / 5  C) 7 / 15  D) 4 / 15  E) 11 / 30

Rationale: "number of multiples of 2 from 1 through 40 = 40 / 2 = 20 number of multiples of 21 from 1 through 40 = 40 / 21 = 1 number of multiples of 2 and 21 both from 1 through 40 = number of multiples of 21 * 2 ( = 42 ) = 0 total favourable cases = 20 + 1 - 0 = 21 probability = 21 / 40 answer : option a"
Answer: A