Question

An automotive researcher wanted to estimate the difference in distance required to come to a complete stop while traveling 40 miles per hour on wet versus dry pavement. Because car type plays a role, the researcher used eight different cars with the same driver and tires. The braking distance (in feet) on both wet and dry pavement is shown below. Test whether there is a difference in stopping distance for wet vs. dry pavement. (Paired Sample)

Car	1	2	3	4	5	6	7	8
Wet	106.9	100.9	108.8	111.8	105.0	105.6	110.6	107.9
Dry	71.8	68.8	74.1	73.4	75.9	75.2	75.7	81.0

Answer 1

Ans:

Car	1	2	3	4	5	6	7	8
Wet	106.9	100.9	108.8	111.8	105	105.6	110.6	107.9
Dry	71.8	68.8	74.1	73.4	75.9	75.2	75.7	81
d	35.1	32.1	34.7	38.4	29.1	30.4	34.9	26.9
d-bar	32.7
sd	3.767

Test statistic:

t=(32.7-0)/(3.767/SQRT(8))

t=24.55

df=8-1=7

p-value=0.0000

Reject the null hypothesis and conclude that  there is a significant difference in stopping distance for wet vs. dry pavement.