Minimum members needed in a club to guarantee at least two have same birth month

A bag contains 5 black and 4 white balls. A man selects two balls at random. What is the probability that both of these are of the same colour?

Three different numbers are selected at random from the first 15 natural numbers. What is the probability that the product of two of the numbers is equal to third number?

Twelve Tickets are numbered from 1 to 12. If one ticket is selected at random, then the probability that the number on the ticket is a multiple of 2 or 3 is :

If four whole numbers are chosen randomly and multiplied, probability that last digit is 1,3,7 or 9?

The tickets numbered from 1 to 20 are mixed up and then a ticket is drawn at random. What is the probability that the ticket has a number which is a multiple of 3 or 5?