There are 9 students participating in a spelling bee. In how many ways can the students who go first¸ second¸ and third be chosen?

Answer 1

first one 9 choices
second one 8 choices
third one 7 choices
9 * 8 * 7
or look up permutations
number of ways to arrange n things taken r at a time
P(n,r) = n! / (n-r)!
here
P(9,3) = 9! /(9-3)! = 9!/6! = 9*8*7 *6!/6! = 9*8*7 again