Efficiency experts study the processes used to manufacture items in order to make them as efficient as possible. One of the steps used to manufacture a metal clamp involves the drilling of three holes. In a sample of 55 clamps, the mean time to complete this step was 52.2 seconds. Assume that the population standard deviation is = 10 seconds. Round the critical value to no less than three decimal places.
(a) Construct a 90% confidence interval for the mean time needed to complete this step. Round the answer to at least one decimal place. A 90% confidence interval for the mean is 52.8 <μ< 64.2 (b) (b) Find the sample size needed so that a 80% confidence interval will have margin of error of 1.5.
A sample size____ is needed in order to obtain a 80% confidence interval with a margin of error of 1.5. Round the sample size up to the nearest integer.