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 number divisible by 5.

Answer 1

Let E₃ be the event of getting a number divisible by 5.

Discs bearing numbers divisible by 5 are 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 and 90.

Number of discs bearing a number divisible by 5 = 18

∴ P(getting a number divisible by 5) = P(E₃) =`("Number of outcomes favourable to"  E_3)/"Number of all possibles outcomes"`

`= 18/90 = 1/5`

Thus, the probability that the disc bears a number divisible by 5 is `1/5`.