Question

A sample of 64 was taken from a population, with the mean of the sample being 119 and the standard deviation of the sample being 16. What is the 68% confidence interval for the mean of the population?

A. (115, 123)
B. (113, 125)
C. (117, 121)
D. (118, 120)

Answer 1

68% is within 1 sigma of mean, so simply find the standard error and work the confidence interval

Answer 2

standard error = 16/sqrt(64) = 16/8 = 2

Answer 3

therefore the confidence interval would be 2 units away from mean :
\[(119-2,~~119+2) ~~~= ~~~(117,~~121)\]