math213

Say you have 12 books, but room to display only 7. I will open this to everyone - how many differnt arrangements are there if the order of the books matters (permutation) and how many if order is of no consequence (combination)?

asked by brina
  1. lajnklh

    posted by Anonymous
  2. If the order does matter than the number of permutations is 12*11*10*9*8*7*6= P(12,7) = 3991680

    if the order does not matter (combinations)
    it would be 12!/(7!5!) = C(12,7) = 792

    both P(n,r) and C(n,r) can be found on a standard scientific calculator
    usually they are labeled nPr and nCr

    to do C(12,7)
    enter
    12
    2nd F
    nCr
    7
    =

    you should get 792

    posted by Reiny

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