A telephone company's records indicate that private customers pay on average $17.10 per month for long-distance telephone calls. A random sample of 10 customers' bills during a given month produced a sample mean of $22.10 expended for long-distance calls and a sample standard deviation of $6.71. Test at 5% significance level to determine if the mean level of billing for long distance calls per month is in excess of $17.10.

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