Specify the number of ways to perform the task described Giv

Specify the number of ways to perform the task described. Give your answers using P(n, r) or C(n, r) notation. Mulder will read the files on seven unsolved cases from a list of thirteen. He does not care about the order in which he reads the files. The number of ways to perform the task is nothing.

Solution

If order does not matter, this is a combination problem, not one of permutations.

The questions is, how many combinations of 7 files can be selected from 13?

n = 13 ; r = 7

13C7 = 13!/(13 -7)!(7!)

=13!/8!7!

= 1716 ways