In an experiment on braking performance, a tire manufacturer measured the stopping distance for one of its tire models. On a test track, a car made repeated stops from 60 miles per hour. Twenty tests were run, 10 each on both dry and wet pavement, with results shown in the accompanying table. (Note that the actual braking distance, which takes into account the driver's reaction time, is much longer, typically near 300 feet at 60 mph!) Complete parts a and b below.

Dry Pavement	Wet Pavement
143	210
152	192
142	219
142	207
132	197
147	208
127	207
141

a)	Find a 95% confidence interval for the mean dry pavement stopping distance. Be sure to check the appropriate assumptions and conditions, and explain what your interval means.

Select all the appropriate assumptions and conditions.

A.

The dry pavement stops were made under different conditions and not paired in any way. The independent groups assumption is satisified.

B.

A Normal probability plot of the stopping distances is roughly straight. The nearly Normal condition is satisfied.

C.

These stops are probably representative of all such stops for this type of car, but not for all cars. The randomization condition is satisfied.

Part 2We are 95% confident that the mean stopping distance for this type of car on dry pavement is between

enter your response here

and

enter your response here

feet.(Round to one decimal place as needed.)Part 3

b)	Find a 95% confidence interval for the mean increase in stopping distance on wet pavement. Be sure to check the appropriate assumptions and conditions, and explain what your interval means.

Select all the appropriate assumptions and conditions.

A.

The histogram of wet pavement stopping distances is approximately Normal with no outliers. The nearly Normal condition is satisfied.

B.

These stops are probably representative of all such stops for this type of car, but not for all cars. The randomization condition is satisfied.

C.

The wet pavement stops and dry pavement stops were made under different conditions and not paired in any way. The independent groups assumption is satisified.

Part 4We are 95% confident that the mean increase in stopping distance for this type of car on wet pavement is between

enter your response here

and

enter your response here

feet.(Round to one decimal place as needed.)