We will use permutations from the previous section to see what is going on.

There are `P_4^26` ways of arranging any `4` letters chosen from the alphabet (where the order is important):

`P_4^26` `=(26!)/((26-4)!)` `=(26!)/(22!)` `=358800`

But in this question, the order is not important. Any set of `4` letters chosen can be arranged in `4!` ways.

Hence, the number of different sets of `4` letters is

`(P_4^26)/(4!)=358800/24=14950`