We have 20 ways to pick the president.
And, after he/she is chosen, 19 ways to pick the vice-president.
And then, 18 ways to pick a treasurer.
So 20 x 19 x 18 = 6840 different ways
We could also find this answer by using a permutaion .... P(20,3) = 6840 .... OR ....by counting sets
C(20,3) = 1140 possible sets of 3 different people.....but.....each set can be arranged in 3! = 6 ways.
So ... 1140 x 6 = 6840
I always like this last one best......we have two tasks .... 1) pick all of the possible different sets, 2) arrange each of these in all possible ways.....
