(Solved): A special bumper was installed on selected vehicles in a large fleet. The dollar cost of body repa ...

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 Mean Damage Test Group = $1,101 Control Group = $ 1,766 Sample Standard Deviation 52 = $ 838 $1 = $ n? = Repair Incidents n? = 9 Source: Unpublished study by Thomas W. Lauer and Floyd G. Willoughby. (a) Construct a 90 percent confidence interval for the true difference of the means assuming equal variances. (Round your answers to 3 decimal places. Negative values should be indicated by a minus sign.) The 90% confidence interval is from The 90% confidence interval is from (b) Repeat part (a), using the assumption of unequal variances with Welch's formula for d.f. (Round your answers to 2 decimal places. Negative values should be Indicated by a minus sign.) O Yes No 696 12 Mean Damage x bar, = $1,101 xbar? = $1,766 to (c) Did the assumption about variances change the conclusion? Confidence Interval to (d) Construct separate 90% confidence intervals for each mean. (Round your answers to 2 decimal places.) } (