Lifetime of electronics: In a simple random sample of 100 electronic components produced by a certain method, the mean lifetime was 125 hours

Lifetime of electronics: In a simple random sample of 100 electronic components produced by a certain method, the mean lifetime was 125 hours. Assume that component lifetimes are normally distributed with population standard deviation 0' = 20 hours. Round the critical value to no less than three decimal places. (a) Construct an 80% con?dence interval for the mean battery life. Round the answer to the nearest whole number. An 80% con?dence interval for the mean battery life is < u < -. (b) Find the sample size needed so that a 95% con?dence interval will have a margin of error of 4. A sample size of D is needed so that a 95% confidence interval will have a margin of error of 4. Round the sample size up to the nearest integer.