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Thread: Confidence interval by hand

  1. #1
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    Confidence interval by hand

    Hi, really can't figure out this as it needs to be solved by hand (to be used orally). I only have an idea of how to nspire. Therefore, I hope there is a genius that can solve it in the head / or know the formula. Thanks in advance!


    A normally distributed stochastic variable X has mean value and standard deviation σ. A sample of 100 measurements gave a 95% confidence interval, the width of which was 3.92


    1) Determine σ
    2) How many measurements should be made if the 95% confidence interval should have a width of no more than 2
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  2. #2
    MHF Contributor
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    Re: Confidence interval by hand

    Always, with Normal Populations, $\displaystyle n = \dfrac{z^{2}\cdot s^{2}}{d^{2}}$
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  3. #3
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    Re: Confidence interval by hand

    What is d?
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