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How large a sample of U.S. adults is needed in order to estimate U with a 95% confidence interval of length 1.2 hours?

  • Statistics -

    I assume this was part of your previous post:

    A study was conducted in order to estimate u, the mean number of weekly hours that U.S. adults use computers at home. Suppose a random sample of 81 U.S. adults give a mean weekly computer usage time of 8.5 hours and that from prior studies , the population standard deviation is assumed to be 3.6 hours.

    If so, use this formula:

    Margin of error = z-value * sd/√n

    With your data:

    1.2 = 1.96 * 3.6/√n

    Solve for n.

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