math213

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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)?

  • math213 -

    lajnklh

  • math213 -

    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

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