Class-12 || Permutation and Combination ~ Basic principles of counting || Basic mathematics || Full Notes

Before commencing the Chapter Combination and Permutation, Let us get acquainted with the concept of "Basic Principle of Counting"

The Basic Principle Of Counting 

This principle can be best understood with some examples.Let us consider three letters A, B, C and see in how many ways they can be arranged in a row.

                                     ABC                    BCA                    CAB

                                     ACB                    BAC                    CBA

Thus we see that they can be arranged in six ways. This can be explained in a simple way. When we choose a first letter we can choose anyone of the three.So there are three choices.For each choice of the first letter there are only three letters left from which we have to choose the second letter. So these first two letters can be choosen in 3.2 =6 ways.For th ethird choice there is no alternative but to choose the letter left.Thus we have 3.2.1=6 possibilities.

   This consideration leads us to the principle known as Basic Principle of counting.