89. Stopping distance. 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 following table. (Note that actual braking distance, which takes into account the driver’s reaction time, is much longer, typically nearly 300 feet at 60 mph!)

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.

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.

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Stopping Distance (ft) Dry Pavement | Wet Pavement 145 211 152 191 141 220 143 207 131 198 148 208 126 206 140 177 135 183 133 223