The lifetime of a new brand of clock battery is normally distributed with a mean of 8,200 hours and a variance of 2,500 hours.
A random sample of 40 clock batteries of this brand was selected.
1) What is the probability that the sample mean lifetime will be between 8,210 and 8,220 hours?
2) There is the probability of 0.95 that the sample mean lifetime will be less than t hours.What is the value of t?