Answer
65780
Work Step by Step
A set of five letters can be selected from the English alphabet in C(26, 5) ways. [By the definition of C(n, r) ]
C(26, 5) = $\frac{26!}{(26-5)!5!}$ [C(n, r) = $\frac{n!}{(n-r)!r!}$ ]
= $\frac{26!}{(21)!5!}$
=$\frac{26\times25\times24\times23\times22\times21!}{21!5!}$
=$\frac{26\times25\times24\times23\times22}{5!}$
=65780 ways