Question

A box contains 90 discs which are numbered 1 to 90. If one disc is drawn at random from the box, find the probability that it bears a number divisible by 5 and greater than 50.

Answer 1

Total number of discs = n(S) = 90

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

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

The probability that it bears a number divisible by 5 and greater than 50 is 55, 60, 65, 70, 75, 80, 85 and 90.

∴ n (B) = 8

∴ P (B) = `("n"("B"))/("n"("S")) = 8/90 ~~ 4/45`