55 people are randomly selected and the accuracy of their wristwatches is checked, with positive errors representing watches that are ahead of the correct time and negative errors representing watches that are behind the correct time. The 55 values have a mean of 51sec and a standard deviation of 220sec. Use a 0.01 significance level to test the claim that the population of all watches has a mean of 0sec. (Assume \sigma = 220sec.)

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