Does the Gas Leakage Rate from Automobile Tires Depend on the Type

Multiple Choice

Does the gas leakage rate from automobile tires depend on the type of gas used to fill them? A sample of automobile tires are filled with nitrogen to a pressure of 1 atmosphere, and the time is measured for the internal pressure to fall to 0.9 atmospheres. The experiment is repeated for this sample of tires, but using sulfur hexafluoride in place of nitrogen. The results are summarized below. The null hypothesis is that the difference in mean population leak times is zero. Calculate a 95% confidence interval for the mean of population differences in leak times. Assume the leak times are normally distributed.

A) (-5.07, -3.47)
B) (-8.65, 0.12)
C) (-9.86, 1.33)
D) (-9.15, 0.61)