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Suppose that an accounting firm does a study to determine the time needed to complete one person's tax forms. It randomly surveys 125 people. The sample mean is 23.1 hours. There is a known population standard deviation of 6.2 hours. The population distribution is assumed to be normal. NOTE: If you are using a Student's t-distribution, you may assume that the underlying population is normally distributed. (In general, you must first prove that assumption, though.) + Part (a) + Part (b) + Part (c) Part (d) Construct a 90% confidence interval for the population mean time to complete the tax forms. (i) State the confidence interval. (Round your answers to two decimal places.) (ii) Sketch the graph. (Round your answers to two decimal places.) C.L. = = X (ii) Calculate the error bound. (Round your answer to two decimal places.)