Question: Public Policy and Political Science Residential mailboxes in Des Moines, Iowa, should be installed such that the bottom of the mailbox is 42 inches above the ground. This rule is designed for safety and to accommodate short mail carriers. A random sample of 75 mailboxes in the city was selected. The height of each was carefully measured, and the sample mean was 43.22 inches. Assume σ =7.6 inches and use a = 0.05. Is there any evidence to suggest the true mean height of mailboxes in Des Moines is different from 42 inches?