Algebra
posted by Tiff on .
It's been so long since I've donw combinations, and now I have a question about them in my algebra homework packet. Question is....Marcie has a collection of 9 DVDS. She will choose 4 of them to take in the car to watch during a long trip. How many combinations of 3 DVDS can Marcie take from her collection ? 504, 252, 168, or 84 ?

Please clarify if she is taking 3 or 4. You say both numbers.
If she is taking 4, the answer is
9!/(4!*5!) = 9*8*7*6/(1*2*3*4)
= 9*8*7/4 = 126
If she is taking 3, the answer is
9!/(3!*6!) = 9*8*7*6/3! = 9*8*7 = 504