Posted by Mel on .
If the average commute time is 10.9 miles, but the average is actually the mean of a sample of 300 commuters and the sample standard deviation is 6.2 miles Estimate the true mean commute distance using 99% confidence level.

statistics 
Kuai,
10.9  +2.575 *6.2/√300
10+ 0.9217
= (9.98, 11.82)