Question 249375
one professor grades homework by randomly choosing 5 out of 15 homework problems to grade. How many different groups of 5 problems can be choosen from the 15 problems?

The formula for combinations of k things taken from n things is:

C(n,k) = n!/((k!*(n-k)!)

In this case n = 15 and k = 5 so we have:

C(15,5) = 15!/(5!*10!)

You will need to multiply out the factorials and finish the calculation for the final answer.