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The ages of commercial aircraft are normally distributed with a mean of 13.0 years and a standard deviation of 7.5 years what percentage of individual aircraft have ages greater than 15 years assume that a random sample of 49 aircraft is selected and the mean age of the sample is computed. What percentage of sample means have ages greater than 15 years

  • statistics -

    For the individual aircraft,

    Z = (score-mean)/SD

    Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to the Z score. Multiply by 100.

    For the mean,

    Z = (score-mean)/SEm

    SEm = SD/√n

    Use the same table.

  • statistics -

    43

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