A sports writer wished to see if a football filled with heli

A sports writer wished to see if a football filled with helium travels farther, on average, than a football filled with air. To test this, the writer used 20 adult male volunteers. These volunteers were randomly divided into two groups of 10 subjects each. Group 1 kicked a fotball 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 xbar 1=32yards, with a standard deviation s1=9 yards. The mean yardage for group 2 was xbar 2=27 yards, with a standard deviation s2=6 yards. Assume the two groups of kicks are independent. Let u1 and u2 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-filled and an air-filled football. Assume that two-sample t procedures are safe to use. A 99% confidence interval for u1-u2 is (using the conservative value for the degrees of freedom)

a. -0.7 to 10.5 yards

b. -6.7 to 16.7 yards

c. -3.8 to 13.8 yards

d. -6.1 to 16.1 yards

Solution