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Math Help - Probability

  1. #1
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    Probability

    This problem deals with probability, and I am having trouble contemplating and establishing what is I need to do for this problem...

    A box contains eight balls numbered 1 to 8. A ball is selected and the replaced. A second ball is drawn. What is the probability of drawing the number 2 first and then the number 7?

    The chance of drawing a number 2 the first time is 1/8 right?
    And isn't the chance to draw a number 7 after that equally 1/8? However I know this is far from the right answer, can someone explain to me what I did wrong and walk me through the necessary steps or at least an explanation of the formula to use and why?
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  2. #2
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    Quote Originally Posted by Murphie View Post
    This problem deals with probability, and I am having trouble contemplating and establishing what is I need to do for this problem...

    A box contains eight balls numbered 1 to 8. A ball is selected and the replaced. A second ball is drawn. What is the probability of drawing the number 2 first and then the number 7?

    The chance of drawing a number 2 the first time is 1/8 right?
    And isn't the chance to draw a number 7 after that equally 1/8? However I know this is far from the right answer, can someone explain to me what I did wrong and walk me through the necessary steps or at least an explanation of the formula to use and why?
    Yes you are correct, when the ball is replaced the probability of drawing the 7 is also \frac{1}{8}, as the problem asks what is the probability of drawing a 2 AND then a 7, we multiply the probabilities because of the "AND", so

    \frac{1}{8}*\frac{1}{8}=\frac{1}{64}
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