How many samples?

Here's a question: how many samples of size 3 can you draw from a population of 5? Here n = 3 and N = 5.
The formula is N!/n! * (N-n)! The ! means 'factorial'. You multiply out the number followed by all the integers smaller than the number. So 3! = 3 * 2 * 1 = 6. It's a shorthand.

To answer this question: the number of different samples that can be drawn is
5!/3!(5-3)! = 120/6* 2 = 10

Note that there is a ! key on most calculators. You might want to practice a bit.