Permutations and Combinations: Lecture 2

In this lecture, you learn about combinations.

1. Notation of combinations and what does it mean?

If you choose r objects from n distinct objects disregard of the order of choosing, the no. of combination is represented by \[_{}^{n}\textrm{C}_{r}\]

Do you realise that combination notation is also used in binomial expansion? Why is it so?


2. Relationship between permutation and combination

\[_{}^{n}\textrm{P}_{r}={}^{n}\textrm{C}_{r}\times r!\]

Permutation means that the order of choosing is important while for combination the order is not important. Hence, the no. of ways of permutation with r objects chosen from n distinct objects is equivalent of the no. of ways of choosing r objects disregard of the order multiply by the no. of ways to arrange the r objects in order.

After this lecture, you can do tutorial 12.