A survey of 51 randomly selected iPhone owners showed that the purchase price has a mean of $424 with a sample standard deviation of $180.

a. Compute the standard error of the sample mean. (Round the final answer to the nearest whole number.)

Standard error $

b. Compute the 80% confidence interval for the mean. (Round the final answers to 2 decimal places.)

The confidence interval is between $ and $ .

c.How large a sample is needed to estimate the population mean within $14 at a 80% degree of confidence?(Round the final answer to the nearest whole number.)

Sample size