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Math Help - probability problem

  1. #1
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    probability problem

    I cant remember how to solve these.

    A computer password consists of eight letters. How many passwords are possible? Assume there is no difference between lower-case and upper-case letters.

    Please help!
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  2. #2
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by sevenlovesyou View Post
    I cant remember how to solve these.

    A computer password consists of eight letters. How many passwords are possible? Assume there is no difference between lower-case and upper-case letters.

    Please help!
    What we are dealing with here is a permutation.

    Recall that _nP_r=\frac{n!}{(n-r)!} where r\leq n.

    Since the password can contain only letters, and we are to assume that there is no difference between lower and upper case we must let n=26 [if there was a difference between upper and lower case, n=52]. Since the password can only be 8 letters long, let r=8.

    So we see that we now have _{26}P_8=\frac{26!}{18!}

    Can you take it from here?

    --Chris
    Last edited by Chris L T521; August 16th 2008 at 04:01 PM.
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  3. #3
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    It has been my experience that passwords allow for repetitions, such as “youuttta”.
    In that case the answer would be {26}^8.
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