Carey has 30 CDs and wants to take pick out 5 to put into her CD player. How many different combinations of CDs can she pick out?

C (30, 5)

C (25, 5)

30!

The correct answer is C (30,5)

That's because you have to know factorials and apply the formulas to find out that:

30! / [5! (30 - 5!) ]

30! / (5! * 25!), which means that there are 142506 combinations, or C (30,5)