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A class survey in a large class for first-year college students asked, "About how many minutes do you study on a typical weeknight?" The mean response of the 463 students was x = 118 minutes.

Suppose that we know that the study time follows a Normal distribution with standard deviation σ = 65 minutes in the population of all first-year students at this university.

Use the survey result to give a 99% confidence interval for the mean study time of all first-year students.

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3 answers
  1. 95% = mean ± 2.575 SEm

    SEm = SD/√n

    I'll let you do the calculations.

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  2. Suppose x has a distribution with μ = 11 and σ = 5.
    (a) If a random sample of size n = 45 is drawn, find μx, σ x and P(11 ≤ x ≤ 13). (Round σx to two decimal places and the probability to four decimal places.)

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  3. It is 99%, sorry for the typo.

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