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Math Help - What Should the Sample Size be?

  1. #1
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    What Should the Sample Size be?

    A chemist who has prepared a product designed to kill a particular type of insect wants to evaluate the kill rate of her preparation.

    What sample size should she use if she wishes to be 95% confident that her experimental results fall within 0.02 of the true fraction of insects killed?

    This is what I did to solve the problem. I am wondering if it is correct?

    Let x be a true fraction.
    alpha = 0.05
    alpha/2 = 0.025
    so, z = 1.96

    sqrt(n)
    z / 0.02 = 98

    n
    9604

    so, n = 9604
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  2. #2
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    Re: What Should the Sample Size be?

    Actually, I redid the problem above using the equation:

    n = z^2 / (4*E^2)

    So, z = 1.96, E = 0.02

    Inserting those values into the equation, we'd get:

    n = (1.96^2) / [4*(0.02^2)] = 2401

    I was wondering if this was correct, not what I did previously.
    Last edited by AwesomeHedgehog; April 12th 2014 at 12:16 PM.
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  3. #3
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    Re: What Should the Sample Size be?

    Yes the second attempt is correct as you remembered to include the standard deviation (or worst case of it)
    Thanks from AwesomeHedgehog
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