On Tuesday after Thanksgiving, a market research firm took a simple random sample of 300 City College students. On average, the students in the sample spent $250 on Black Friday, with standard deviation $54. It was found that 168 of the students in the sample had made at least on internet purchase on Cyber Monday.
a) Find a 95% confidence interval for the average amount spent by all City College students on Black Friday.
b) Find a 90% confidence interval for the percentage of all City College students who made at least one internet purchase on Cyber Monday.