A new brand of laptop battery is produced by ZELCO. The company claims that the battery will last for an extended period of time before a recharge is necessary. A sample of 40 batteries is tested for the length of usage time to recharge. The sample results are as follows:
Sample Size = 40
Sample Mean = 6.5 hrs.
Sample Standard Deviation = 1.3 hrs.
a. Construct a 99% confidence interval for the average length of usage time to recharge.
b. Interpret this interval.
c. How large a sample size will need to be selected if we wish to have a 99% confidence interval with a margin for error of .25 hours?