=+9.61 The McClatchy News Service (San Luis Obispo Telegram-Tribune, June 13, 1991) reported on a study of violence on television during primetime hours. The following table summarizes the information reported for four networks:

Mean Number of Network Violent Acts per Hour ABC 15.6 CBS 11.9 FOX 11.7 NBC 11.0 Suppose that each of these sample means was computed on the basis of viewing n 5 50 randomly selected primetime hours and that the population standard deviation for each of the four networks is known to be s 5 5.