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A bicycle lock has a 4-digit combination. Each of the digits is a number from 0 to 9. Find the probability that the lock has a combination in which 3 of the 4 digits are 3s

  • Math -

    I will assume that repeats are allowed as in most combination locks
    so number of possible codes = 10^3 = 1000

    So we want three 3's and one non-3
    x333---> where x is a number other than 3
    so there are 4(9) of these or 36

    so prob of our event = 36/1000 = 9/250

  • Math -

    Reiny was close, I would adjust the possible combination to 10^4 = 10,000

    So 36/10,000 = 9/2,500

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