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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.
Solution
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`.
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