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Math Help - probality of combination lock HELP!!

  1. #1
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    probality of combination lock HELP!!

    A small combination lock has 3 wheels, each labeled with the 10 digits from 0-9. If an opening combination is a particular sequence of 3 digits with no repeats, what is the probability of a person guessing the right combination.

    The answer in the back of my book says 1/P 10,3 = .0014

    How did they get that I keep getting 720 when I permutaation 10P3.. what do I do
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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: probality of combination lock HELP!!

    There is only 1 right combination, but 10\cdot9\cdot8=720 possible combinations, so the probability in question is:

    P(X)=\frac{1}{720}=0.0013\bar{8}\approx0.0014
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  3. #3
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    Re: probality of combination lock HELP!!

    Thank you so much I didn't round that was my issue.. been at it for a while and you cleared it up good post
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  4. #4
    MHF Contributor MarkFL's Avatar
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    Re: probality of combination lock HELP!!

    Yes, you did it correctly, so I wanted to show another approach, and at the same time imply that rounding was the only issue.
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