Probability (C10)

A box contains cards numbered from 1 to 20. A card is drawn at random from the box. Find the probability that number on the drawn card is

  1. a prime number
  2. a composite number
  3. a number divisible by 3

Answer

(i) Prime numbers from 1 to 20 are 2, 3, 5, 7, 11, 13, 17, 19 i.e. 8

P(prime number) = 8/20 or 2/5

(ii) Composite number from 1 to 20 are 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20 i.e. 11

P(Composite number) = 11/20

(iii) Number divisible by 3 from 1 to 20 are 3, 6, 9, 12, 15, 18 i.e 6

P(number divisible by 3) = 6/20 or 3/10