Efficiency experts study the processes used to manufacture i

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 84 clamps, the mean time to complete this step was 46.8 seconds. Assume that the population standard deviation is 9 seconds. What is the lower bound of the 98% confidence interval?

Round your answer to one decimal place (for example: 41.9). Write only a number as your answer.

The ZInterval command on the TI-84 PLUS Calculator will compute the confidnece interval for the mean when the population standard deviation is known.

Solution

Given a=1-0.98=0.02, Z(0.02) =2.05 (from standard normal table)

So the lower bound of the 98% confidence interval is

xbar- Z*s/vn =46.8 - 2.05*9/sqrt(84)

=44.8