# math check

posted by
**tom9**
.

While writing an article on the high cost of college education, a reporter took a random sample of the cost of new textbooks for a semester. The random variable x is the cost of one book. Her sample data can be summarized by the following. (Give your answers correct to two decimal places.)

n = 21, Óx = 3635.6, and Ó(x - x)2 = 9750.4

(a) Find the sample mean, x.

$ 173.12 .

(b) Find the sample standard deviation, s.

$ 22.08 .

(c) Find the 90% confidence interval to estimate the true mean textbook cost for the semester based on this sample.

Lower Limit $164.30 .

Upper Limit $ 181.94