How many integer must we select to ensure that 3 of them end

Solution

Probabiity of any digit at ones place in an integer is 1/10. Since any of the digits (0-9) can come at ones place,the probability that 3 intergers end in same digit is 10 x (1/10)³ = 0.01.

Since there is 1% chance that, out of integers we select, 3 of them end in the same digit. Therefore, we must select 100 integers to ensure that 3 of them end in the same digit
.