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

(a)A two-digit number (b) a number divisible by 5

Answer 1

Total number of discs in the box = 90

(a) Two digit numbers from 1 to 90 = 81

P(getting a two-digit number) = 81/90 = 9/10

(b) Numbers divisible by 5 from 1 to 90 = 5, 10, …. , 90,

Total numbers = 18

P(getting a number which is divisible by 5) = 18/90 = 1/5