A manufacturer claims that the mean lifetime of its lithium batteries is 1400 hours. A homeowner selects 25 of these batteries and finds the mean lifetime to be 1380 hours with a standard deviation of 80 hours. Test the manufacturers claim. Use alpha = 0.05. Round the test statistic to the nearest thousandth. Write the null and alternative hypotheses. Use the p-value method to vote for the null or the alternative hypothesis.

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  1. Ho: mean = 1400
    Ha: mean < 1400

    Z = (score-mean)/SEm

    SEm = SD/√n

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

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  2. Additional related question.

    If this same question states that the manufacture claim is greater than 1200 hours would the alternative hypothesis be ...
    Ha: mean>1200

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