Question
A special bumper was installed on selected vehicles in a large fleet. The dollar cost of body repairs was recorded for all vehicles that were
A special bumper was installed on selected vehicles in a large fleet. The dollar cost of body repairs was recorded for all vehicles that were involved in accidents over a 1-year period. Those with the special bumper are the test group and the other vehicles are the control group, shown below. Each "repair incident" is defined as an invoice (which might include more than one separate type of damage).
Statistic Test Group Control Group
Mean Damage X1 = $ 1,153 X2 = $ 1,751
Sample Std. Dev. s1 = $ 663 s2 = $ 820
Repair Incidents n1 = 16 n2 = 14
(a)Construct a 99 percent confidence interval for the true difference of the means assuming equal variances.(Round your final answers to 3 decimal places.Negative values should be indicated by a minus sign.)
The 99% confidence interval is from__________to__________
(b)Repeat part (a), using the assumption of unequal variances with Welch's formula ford.f.(Round the calculation for Welch's df to the nearest integer. Round your final answers to 3 decimal places. Negative values should be indicated by a minus sign.)
The 99% confidence interval is from ________to_________
(c)Did the assumption about variances change the conclusion?
Yes
No
(d)Construct separate 99% confidence intervals for each mean.(Round your intermediatetcritvalue to 3 decimal places. Round your final answers to 2 decimal places.)
Mean Damage Confidence Interval
x1=$1,153 ($_______, $________)
x2=$1,751 ($_______, $________)
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