The lengths of my last 12 phone calls have been roughly 3, 8, 3, 5, 1, 13, 9, 2, 7, 3, 13, and 2 minutes. long experience suggests that the standard deviation is about 5 minutes.
a) i am asked what the average length of one of my phone calls is, and i shall estimate it by ; calculate this estimate and give its standard deviation (standard error).
b) assuming this is a large enough sample, write down a 98% confidence interval for the true value μ.