Q. Define Multiplication Rule in probability?

Ans.

A family has two girls, Ann and Barb, and three boys, Carl, David and Earl, in it. In how many ways can the mother pick one boy and one girl to help her with the laundry? We can list all of the possibilities in a tree diagram.

There are 2 x 3 ways to choose one girl and one boy. This is no coincidence, in fact it is the multiplication rule!

In general, suppose we can do job 1 in p ways and an unrelated job 2 in q ways. Then we can do both job 1 and job 2 in p x q ways.