The lifetime of a certain type of battery is known to be normally distributed with standard deviation is 20 hours. A sample of 50 batteries had a mean lifetime of 120.1 hours. It is desired to construct a 95% confidence interval for the mean lifetime for this type of battery. Find
A: what is the point estimated?
B: find the critical value.
C: find the standard error.
D: find the margin of error.
E: construct the 95% confidence interval.
F: is it likely that the population mean u is greater than 130.