# Paired t test & Confidence Interval

A maintenance manager must test a new repair method that should increase the expected time between repairs. For each machine used in the study, she recorded the last time between failures prior to using the new method, which she called "Current," and the first time between failures after using the new, which she called "New." These are the times (in hours):

Machine New Current

1 211 155

2 345 222

3 419 346

4 274 287

5 244 115

6 420 389

7 319 183

8 505 451

9 396 140

10 222 252

a. Conduct the most appropriate hypothesis test using a 0.05 significance level.

b. Construct a 95% confidence interval for the true mean difference.

c. What did you assume to do the analyses? Can you evaluate how well these data meet the assumptions? If yes, determine how comfortable you are with them. If not, explain why.

See attached file.

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#### Solution Summary

The solution provides step by step method for the calculation of testing of hypothesis and confidence interval. Formula for the calculation and Interpretations of the results are also included. Interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.