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Math

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A password consists of 2 letters and 2 digits (0-9). The letters and digits cannot be repeated. How many passwords are possible?

  • Math -

    C=27!/25! * 10!/8! * 4!/2!2!

    The last term represents the number of permuations of two letters, two numbers can be done (six ways).

  • Math -

    my approach:
    first lets choose 2 letters and 2 numbers,
    that is C(26,2)*C(10,2)
    = 325*45
    = 14625

    let's consider one of these, say, DK45
    now that could be arranged in 4! ways

    so the total number of passwords is
    14625*4! = 351000

    bobpursley, when did they introduce that 27th letter?

  • Math -

    A student can create a 3 digit computer password from the numbers 0 to 9. If the digits cannot be repeated, what is the probability of someone guessing the correct password?

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