The mean tax-return preparation fee h&r block charged retail

The mean tax-return preparation fee H&R Block charged retail customers in 2012 was $183 (The Wall Street Journal, March 7, 2012). Use this price as the population mean and assume the population standard deviation of preparation fees is $50.

Round your answers to four decimal places.

a.  What is the probability that the mean price for a sample of 30 H&R Block retail customers is within $8 of the population mean?
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b.  What is the probability that the mean price for a sample of 50 H&R Block retail customers is within $8 of the population mean?
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c.  What is the probability that the mean price for a sample of 100 H&R Block retail customers is within $8 of the population mean?
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d.  Which, if any, of the sample sizes in parts (a), (b), and (c) would you recommend to have at least a .95 probability that the sample mean is within $8 of the population mean?