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Math Help - PROBABILITY problems help please

  1. #1
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    PROBABILITY problems help please

    1) A five-digit number is created using the digits 1-5 each once. What is the probability that the number is odd? Express your answer as a common fraction.

    2) The sum of the digits of a number is 9. What is the
    probability that the number is prime?
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  2. #2
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    #1:

    \frac{5^{4}\cdot 3}{5^{5}}=\frac{3}{5}

    As Plato pointed out, I made a mistake and overlooked your problem said, 'each digit appears once'. Instead of deleting it, let's just say this is the case where the digits repeat.
    Last edited by galactus; October 2nd 2009 at 01:50 PM.
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  3. #3
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    Quote Originally Posted by sri340 View Post
    1) A five-digit number is created using the digits 1-5 each once. What is the probability that the number is odd? Express your answer as a common fraction.

    2) The sum of the digits of a number is 9. What is the
    probability that the number is prime?
    Quote Originally Posted by galactus View Post
    #1:
    \frac{5^{4}\cdot 3}{5^{5}}=\frac{3}{5}
    That answer is for numbers with repeated digits.
    The problem says "each once".
    Try \frac{4!\cdot 3}{5!}

    #2 hint If the sum of the digits is multiple of three the the number is divisiable by three.
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  4. #4
    Eater of Worlds
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    Oh, I overlooked that.

    Thanks.
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