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Homework Help: Finding sample size given info on confidence interval

  1. Jun 28, 2014 #1
    1. The problem statement, all variables and given/known data

    Suppose that an investigator believes that virtually all values in the population are between 38 and 70. The appropriate sample size for estimating the true population mean within 2 units with 95% confidence level is approximately how much?

    2. Relevant equations

    Variance of the sampling distribution of size n = Variance of the population distribution / n

    3. The attempt at a solution

    I think I'm solving
    1.96(SD of the sampling distribution of size n)=2

    But I don't think there's any information given on the population variance so I don't know what to do.
  2. jcsd
  3. Jun 28, 2014 #2
    Worst case, half the population values are 38 and half are 70. What's the variance in that case?
  4. Jun 29, 2014 #3


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    Homework Helper

    Use the three standard deviation rule.
  5. Jun 29, 2014 #4
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