Do quarterbacks matter? How important is the quarterback's skill to the success of an NFL foot- ball team? One way to measure a quarterback's effectiveness is with the "quarterback rating," a complex calculation based on passing accuracy and yardage, touchdown passes, and interceptions. If we create a least-squares linear regression model for AFC teams relating y = team wins during the 2013 season to x = the overall quarterback rating for the team's quarterbacks, we get the following residual plot. 3 2- 1 Residual -1 -2- -3 -5 60 70 80 90 100 Quarterback rating 110 120 (a) Use the residual plot to determine whether the regression model is appropriate. (b) Interpret the value s = 2.473 for this model. (c) Interpret the value = 0.457 for this model.

An annual marathon covers a route that has a distance of approximately 26 miles. winning times for this marathon are all over 2 hours. the following data are the minutes over 2 hours for the winning male runners over two periods of 20 years each. earlier period 14 12 15 22 13 10 19 13 9 14 20 18 16 20 23 12 18 17 6 13 recent period 7 11 7 14 8 9 11 14 8 7 9 8 7 9 9 9 9 8 10 8 (a) make a stem-and-leaf display for the minutes over 2 hours of the winning times for the earlier period. use two lines per stem. (use the tens digit as the stem and the ones digit as the leaf. enter none in any unused answer blanks. for more details, view how to split a stem.) minutes beyond 2 hours earlier period 0 1 2 (b) make a stem-and-leaf display for the minutes over 2 hours of the winning times for the recent period. use two lines per stem. (use the tens digit as the stem and the ones digit as the leaf. enter none in any unused answer blanks.) minutes beyond 2 hours recent period (c) compare the two distributions. how many times under 15 minutes are in each distribution