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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 ?

  • Algebra -

    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

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