How large of a sample size is required?

Question

You want to obtain a sample to estimate the average number of hours per week community college students in the United States work at their job while being a full-time student. Based on previous evidence, you believe the population standard deviation is 10. You would like to be 99% confident that your estimate is within 1.5 hours of the true population mean.

Assume that the number of statistics students is unknown, but very large. How large of a sample size is required? 

Answer 1

sample size formula

n = (z-critical * s/error)^2

s is given as 10

error is given as 1.5

z-critical for 99% confidence interval is 2.58.

n = (2.58 * 10/1.5)^2 = 295.84 ~ 296