The Postmaster at the Huntington Post Office Would Like to Compare

Essay

The postmaster at the Huntington Post Office would like to compare the delivery times to two different locations that are the same distance from Huntington. A random sample of letters is to be divided into two equal groups, the first to be delivered to Location A and the second to be delivered to Location B. Each letter will be delivered on a randomly selected day and the number of days for each letter to arrive at its destination is to be recorded. The measurements for both groups are expected to have a range (variability) of approximately 4 days. If the estimate of the difference in mean delivery times is desired to be correct to within 1 day, with probability equal to 0.99, how many letters must be included in each group? (Assume .) Justify your conclusion.