The accompanying time-to-repair (min) data for both high rail and low rail breaks on curved track appeared in the article “Uncertainty Estimation in Railway Track Life-Cycle Cost” (J. Rail Rapid Transit 2009: 285–293). (On a curved track, the high rail is the outer rail with the larger radius, while the low rail is the inner rail with the smaller radius.)

Normal probability plots of both samples show reasonably linear patterns.
a. Construct a comparative boxplot and comment on interesting features.
b. Carry out a test of hypotheses at significance level .10 to decide if there is evidence for concluding that true average repair time for high rails exceeds that for low rails by more than 30 min.
c. Obtain and interpret a confidence interval at the 90% confidence level for the difference between true average repair times for high and low rails.

Transcribed Image Text:

High: 159 120 480 149 270 547 340 43 228 202 240 218 Low: 258 154 216 240 202 202 216 169 75 340