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    vanillagrown's Avatar
    vanillagrown Posts: 1, Reputation: 1
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    #1

    Jan 27, 2008, 05:22 PM
    probability with letters
    How many different four letter passwords can be formed from the A, B, C, D, E, F, and G if no repetition of letters is allowed?
    PolluxCastor's Avatar
    PolluxCastor Posts: 117, Reputation: 5
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    #2

    Jan 27, 2008, 05:23 PM
    This can be solved using permutations.
    jiten55's Avatar
    jiten55 Posts: 105, Reputation: 8
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    #3

    Jan 27, 2008, 11:52 PM
    Look at it like this:

    First letter of the password can be selected in 7 ways, then Second in 6 ways, then 3rd in 5 ways, then fourth in 4 ways.

    Hence: 7*6*5*4 = 840

    OR

    Formula for permutations of r objects out of n

    = nPr = n!/(n -r)! = 7!/3! = 7*6*5*4 = 840
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