Find the mean weight statistics- need help

Question

You measure 32 textbooks' weights, and find they have a mean weight of 70 ounces. Assume the population standard deviation is 6.6 ounces. Based on this, construct a 95% confidence interval for the true population mean textbook weight.

Give your answers as decimals, to two places

I am 95% confident that the mean weight of textbooks is between  and  ounces.

Answer 1

CI = mean +/- z-critical* std dev/square root (sample size), where z-critical is z-value for probability (Z < 0.975)

CI = 70 +/- 1.96 * 6.6/sqrt(32) = 70 +/- 2.29

CI = (67.71,72.29)