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 two-digit number,

Answer 1

Total number of discs = 90 

 Let E₁ be the event of having a two-digit number.

Number of discs bearing two-digit number = 90 − 9 = 81

∴ P(getting a two-digit number) = P(E₁) = `("Number of outcome favourable to"  E_1)/"Number of all possible outcome "`
`= 81/90 = 9/10`

Thus, the probability that the disc bears a two-digit number is `9/10`