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    Statistics: Sample Size, One or Two-tailed Test

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    The American Water Works Association estimates that the average person in the United States uses 123 gallons of water per day. Suppose some researchers believe that more water is being used now and want to test to determine whether it is so.

    They randomly select a sample of Americans and carefully keep track of the water used by each sample member for a day, then analyze the results by using a statistical computer software package. The output is given here. Assume alpha= .05.

    One-Sample Z
    Test of mu= 123 vs > 123
    The assumed standard deviation= 27.68

    N 40
    Mean 132.360
    SE Mean 4.377
    Lower Bound 125.161
    z 2.14
    p 0.016

    a. How many people were sampled?
    b. Was this a one- or two-tailed test?
    c. What was the result of the study?
    d. What decision could be stated about the null hypothesis from these results?

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    Solution Preview

    (a) 40

    (b) One-tailed (Right-tailed) test

    (3) The p- value ...

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