Lifetimes of Engine Control Modules Chin manages the service

Lifetimes of Engine Control Modules Chin manages the service department of a trucking company. Each truck in the fleet utilizes an electronic engine control module. Long-lasting modules are desirable. A preventive replacement program also avoids costly breakdowns. For this purpose it is desirable that the modules be fairly consistent in their lifetimes, so that preventive replacements can be timed efficiently. Chin tested a sample of 20 Brand A modules, and they lasted 48,560 highway miles on the average (mean), with a standard deviation of 2116 miles. The listing below shows how long each of another sample of 20 Brand B modules lasted. Use these data for Exercises 38-40. According to the sampling, which brand of module has the longer average life (in highway miles). Which brand of module apparently has a more consistent (or uniform) length of life (in highway miles)

Solution

38) mean = sum of all/ total number = 975920/20 =48796

this is for brand b while brand A has average = 48560

therefore brand B has the highest mean life

39) standard deviation =

standard dev of A = 2116

WHILE STD DEV OF B = 3538.9

this means brand A has less std dev which means it has the more consistent life.