Suppose that an accounting firm does a study to determine the time needed to com

Question

Suppose that an accounting firm does a study to determine the time needed to complete one person's tax forms. It randomly surveys 175 people. The sample mean is 22.6 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.)

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.)

Explanation / Answer

n = 175 , mean = 22.6 , s = 6.2

z value at 90% CI = 1.645

CI = mean +/- z * (s/sqrt(n))

= 22.6 +/- 1.645 * ( 6.2/sqrt(175))

= (21.83 , 23.37)

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