Scouting an NFL free agent. In seeking a free-agent NFL running back, a general manager is looking for a player with high mean yards gained per carry and a small standard deviation. Suppose the GM wishes to compare the mean yards gained per carry for two free agents, on the basis of independent random samples of their yards gained per carry. Data from last year’s pro football season indicate that s1 2

= s2 2 ≈ 10 yards. If the GM wants to estimate the difference in means correct to within 4 yard with a confidence level of .95, how many runs would have to be observed for each player? (Assume equal sample sizes.)