NCERT Solutions
Class 10 Maths
Probability

Ex.14.1 Q.18
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
(1) a two-digit number.
(2) a perfect square numbers.
(3) a number divisible by 5.
Total number of discs = 90
(1) Total number of two-digit numbers between 1 and 90 = 81
P (getting a two-digit number)
= Number of favourable outcomes ÷ Total possible outcomes = =
(2) Perfect squares between 1 and 90 are 1, 4, 9, 16, 25, 36, 49, 64, and 81.
Therefore, total number of perfect squares between 1 and 90 is 9.
P (getting a perfect square)
= Number of favourable outcomes ÷ Total possible outcomes = =
(3) Numbers that are between 1 and 90 and divisible
by 5 are 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, and 90.
Therefore, total numbers divisible by 5 = 18
Probability of getting a number divisible by 5 = =