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Math Help - Probability Help

  1. #1
    Newbie
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    Nov 2009
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    Probability Help

    I have been sweating buckets over my recent statistics test on probability. It's not coming to me, and my textbook isn't helping me much. I am basically clueless on how to calculate sample size with no preliminary estimate.

    Here is the example I'm pouring over.

    You are a travel agent and wish to estimate, with 95% confidence, the proportion of vacationers who plan to travel outside the United States in the next 12 months. Your estimate must be accurate within 3% of the true proportion. Find the minimum sample size needed if no preliminary estimate is available.

    Any way I can get some help showing how to solve this problem? Any help is greatly appreciated.
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  2. #2
    Eater of Worlds
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    If no preliminary estimate is available, use p=q=.5

    n=pq\left(\frac{z}{E}\right)^{2}=(.5)(.5)\left(\fr  ac{1.96}{.03}\right)^{2}\approx 1067.11

    Round up and get 1068 as the minimum sample size.
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