4. A questionnaire of spending habits was given to a random sample of college students. Each student was asked to record and report the amount of money they spent on textbooks in a semester. The sample of 130 students resulted in an average of $422 with a standard deviation of $57. (2 points)

a. Give a 90% confidence interval for the mean amount of money spent by college students on textbooks.

b. Is it true that 90% of the students spent the amount of money found in the interval from part (a)? Explain your answer.

c. What is the margin of error for the 90% confidence interval?

d. How many students should you sample if you want a margin of error of $5 for a 90% confidence interval?