mean of the battery lifetimes for all phones of their latest model You decide to measure battery lifetime by recording the time it takes for the battery charge to run out while a tester is streaming videos on the phones continuously Then you select a random sample of 45 cell phones of the manufacturer s latest model and record their battery lifetimes Assume that the population standard deviation of the battery lifetimes for that cell phone model using your method of measurement is 2 42 hours Based on your sample follow the steps below to construct a 99 confidence interval for the population mean of the battery lifetimes for all phones of the manufacturer s latest model If necessary consult a list of formulas a Click on Take Sample to see the results from your random sample of 45 phones of the manufacturer s latest model Take Sample Sample size 0 Point estimate Population standard deviation Critical value Enter the values of the sample size the point estimate for the population mean the population standard deviation and the critical value you need for your 99 confidence interval Choose the correct critical value from the table of critical values provided When you are done select Compute Compute 0 00 0 00 Number of phones 2 00 Sample mean Standard error Margin of error 4 00 99 confidence interval Sample standard deviation 99 confidence interval 6 00 X Confidence level 99 95 b Based on your sample enter the lower and upper limits to graph the 99 confidence interval for the population mean of the battery lifetimes for all phones of the manufacturer s latest model 90 Population standard deviation 2 42 8 00 Critical value 20 005 2 576 20 025 1 960 20 050 1 645 10 00 10 00