A 90 % confidence interval (a t interval) for the mean lives (in minutes) of Kodak AA batteries is ( 400, 440 ). Assume that this result is based on a sample of size 15 .

1) What is the value of the sample mean?

2) What is the value of the sample standard deviation?

3) Construct the 99% confidence interval.

4) If the confidence interval (402.7050 ,437.2950) is obtained from the same sample data, what is the degree of confidence?