If one operation can be done in r different ways and a second operation can be done in s different ways,
then the two operations can be done in succession in r times s different ways.
This is called the Multiplication Principle.
This principle can be extended to the case where there are more than two operators. Formally, if a procedure can be broken down into r successive and ordered stages that are independent of each other, and if there are n1 number of outcomes in the first stage,
n2 number of outcomes in the second stage,
n3 number of outcomes in the third stage,
and so on until ‘n r’ number in the r-th stage,
then the total number of outcomes for the whole procedure is ‘n1’ times ‘n2’ times ‘n3’, all the way to times ‘n r’.
Let us see how we can apply this principle on problems.