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Math Help - Tennis probability

  1. #1
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    Tennis probability

    I got a question about probability.....
    The probability that a tennis set will go to a tiebreaker is 14%. In 80 randomly selected tennis sets, what is the mean and std dev. of the number of tie breakers?
    a) mean: 10.4; std dev: 3.1
    b) mean: 10.4; std dev: 3.35
    c) mean: 11.2; std dev: 3.10
    d) mean: 11.2; std dev 3.35

    Thanks everybody
    Last edited by mr fantastic; April 14th 2009 at 04:29 PM. Reason: pms are not sent advising you of the posting of a reply.
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  2. #2
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    We will assume each game is independent and that the probability of a tie is fixed for every game. Then this situation follows a binomial distribution.

    Let X be the number of games with a tie: then X\,~ \,\text{Binomial}\,(80, 0.14)

    For a binomial distribution,

    E(X) = np = 80 \times 0.14

    and

    \sigma_X = \sqrt{np(1-p)} = \sqrt{80 \times 0.14 \times 0.86}
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  3. #3
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    Thanks for your reply, It helped me alot....I'm kinda started to get some concept.....
    Last edited by mr fantastic; April 14th 2009 at 10:17 PM. Reason: Moved question to a new thread.
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