Sample question of permutation and combination.

Question

You can bring along 2 friends! you have 5 friends who want to come along. How many different groups of friends could you take with you?

Answer 1

Here the order of the r elements does not matter, so we will use combination formula:

= $\frac{n!}{r!\left(n-r\right)!}$

= $\frac{5!}{2!\left(5-2\right)!}$

= 10