Question

There are 20 students in a 5th grade class. Four of these students will be selected to be patrols. In how many ways can the four patrols be selected?

Answer 1

4845 different ways

Explanation:

As the order of the patrols doesn't matter, we have a combination problem, where we will form groups of 4 students among a total of 20 students, so we have a combination of 20 choose 4:

C(20, 4) = 20! / (4! * (20 - 4)!) = 20! / (4! * 16!) = 20*19*18*17 / (4*3*2) = 4845

So there are 4845 different ways to select the four patrols.