A phone manufacturer recently reviewed the build time for 25 phones. The sample mean was 18 hours with a standard deviation of 3.15 hours The build times are known to be normally distibuted. If the manufacturer wants to be 95% confident in the sample to represent the population,

What is the t value associated with this level of confidence?Answer

What is the standard error?Answer

What is the confidence interval? (round to one decimal places)

Lower Limit:Answer

Upper Limit:Answer

Suggest an appropriate sample size if the acceptable error is 0.9 hours. Use the sample standard deviation as a pilot study to estimate the population standard deviation.