HW 7: Problem 5 Previous Problem Problem List Next Problem (1 point) Suppose we want a 90% confidence interval for the average amount spent on books by freshmen in their first year at college. The amount spent has a normal distribution with standard deviation $27. How large should the sample be if the margin of error is to be less than $2? ANSWER:HW 7: Problem 6 Previous Problem Problem List Next Problem (1 point) Justin is interested in buying a digital phone. He visited 12 stores at random and recorded the price of the particular phone he wants. The sample of prices had a mean of $191.96 and a standard deviation of $31.74. (a) What critical value t* should be used for a 95% confidence interval for the mean, /, of the distribution? (b) Calculate a 95% confidence interval for the mean price of this model of digital phone: (Enter the smaller value in the left answer box.) Note: Round your answer to 2 decimal places. $ to $ Note: You can earn partial credit on this