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Math Help - Probability Problem

  1. #1
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    Probability Problem

    A student and a professor choose a two digit number. Find the probability that the two choose the same number.



    I'm not sure the best method to solve this or what the answer could be. I do know that it has to be between 10-99.

    Thank you.

    I talked with a friend that said there are 90 possibilities (10-99) and the student picks one two digit number and the professor picks one two digit number.

    1/90 + 1/90= 2/90 and simplified would be ((1/45))that both choose a two digit number.

    Is this correct?
    Last edited by DaddyoSD; March 22nd 2013 at 05:42 PM.
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  2. #2
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    Re: Probability Problem

    I'm just guessing here but wouldn't it depend on how they are picking?

    For instance if one person picked first. Then the odds that the second person picks the same two digit number is 1/90. However what if they pick at the same time? Then this becomes a question of the same event occurring twice. I would look at it like a dice roll. What are the odds that both people roll a 6? Well that is (1/6)^2. What are the odds they both pick the same two digit number? (1/90)^2.

    Might wait for another comment though, my probability engine isn't working well today.
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  3. #3
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    Re: Probability Problem

    Quote Originally Posted by DaddyoSD View Post
    A student and a professor choose a two digit number. Find the probability that the two choose the same number. I do know that it has to be between 10-99.
    I think you you mean that their numbers are from 10 to 99.
    Between means 10<N<99.

    The student can select 90 numbers so can the teacher.
    So the ordered pairs of selections look like (S,P) where 1\le S\le 9~\&~0\le P\le 9
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