Question

A box contains 90 discs which are numbered from 1 to 90. If one disc is drawn at random from the box, find the probability that it bears 

(i) a two-digit number 

(ii) a perfect square number 

(iii) a number divisible by 5.

Answer 1

(i) Number of two digit numbers = 90 – (1, 2, 3, 4, 5, 6, 7, 8, 9) = 81

P(a two-digit number) = 81/90

(ii) Number of perfect squares = 1, 4, 9, 16, 25, 36, 49, 64, 81 = 9

P(a perfect square number) = 9/90

(iii) Numbers divisible by 5 = 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 = 18

P(a number divisible by 5) = 18/90