A teacher wishes to pick a hall monitor and an assistant hall monitor from her class of 22 students. In how many different ways can the selection be made?

Question

Finite math

Answer 1

this is a combination

22 choose 2

use n!/r!(n-r)!

22!/(2!)(22-2)!

22!/(2!)(20)!

(22*21)/2    (the two 20!'s cancel)

11*21=231 ways