Given a class of 11, we need to choose 3 people to be the president, vice-president, and secretary.
That is, we need to pick 3 people out of 11. We can calculate how many ways there are using the combinatory operator, defined as:
In this case, n = 11 and k = 3, then:
There are 165 different ways to choose a president, vice-president, and secretary from a class of 11.