Assume three dierent engineers studied true mean stopping distances at 50 mph for cars of certain kind equipped with two dierent braking systems (each took random samples of different sizes). Supposing that σ1 = σ2, and that braking distances are normally distributed, compute a 90% condence interval for different in mean braking distances for each of following situations:
(a) n1 = 40; n2 = 40; x1 = 115:7; x2 = 129:3; s1 = 5.0; s2 = 5.4
(b) n1 = 10; n2 = 15; x1 = 115:7; x2 = 129:3; s1 = 5.0; s2 = 5.4
(c) n1 = 12; n2 = 34; x1 = 115:7; x2 = 129:3; s1 = 5.0; s2 = 5.4