In Order to Estimate the Average Daily Down Time,a Manufacturer $\pm$

Multiple Choice

In order to estimate the average daily down time,a manufacturer randomly samples 40 days of production records and found a mean of 55.576 minutes and standard deviation of 77.9 minutes.An 80% confidence interval is:

A) 55.6751 $\pm$ .28(12.32) .
B) 55.6751 $\pm$ .304(12.32) .
C) 55.6751 $\pm$ .28(77.9) .
D) 55.6751 $\pm$ .304(77.9) .