A sports writer wished to see if a football filled with helium travels farther when kicked, on average, than a football filled with air. To test this, the writer used 18 adult male volunteers. These volunteers were randomly divided into two groups of nine subjects each. Group 1 kicked a football filled with helium to the recommended pressure. Group 2 kicked a football filled with air to the recommended pressure. The mean yardage for group 1 was = 30 yards with a standard deviation s1 = 8 yards. The mean yardage for group 2 was = 26 yards with a standard deviation s2 = 6 yards. Assume the two groups of kicks are independent. Let ?1 and ?2 represent the mean yardage we would observe for the entire population represented by the volunteers if all members of this population kicked, respectively, a helium and an air-filled football. Assume that two-sample t procedures are safe to use.
A 99% confidence interval for ?1 - ?2 is (use the conservative value for the degrees of freedom)
A. -.7 to 8.7 yards
B. -2.2 to 10.2 yards
C. -7.2 to 15.2 yards
D. -8.7 to 16.7 Yards
A 99% confidence interval for ?1 - ?2 is (use the conservative value for the degrees of freedom)
A. -.7 to 8.7 yards
B. -2.2 to 10.2 yards
C. -7.2 to 15.2 yards
D. -8.7 to 16.7 Yards