The Postmaster at the Harrington Post Office Would Like to Compare

Short Answer

The Postmaster at the Harrington Post Office would like to compare the delivery times to two different locations which are the same number of miles from Harrington. A random sample of letters are to be divided into two equal groups, the first delivered to Location A and the second 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 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 n₁ = n₂ = n.
______________