Question

THE WARRANTY ON THE MOTOR OF A DISHWASHER IS 8 YEARS. IF THE BREAKDOWN TIMES OF THIS MOTOR ARE NORMALLY DISTRIBUTED, WITH A MEAN OF 10.2 YEARS AND A STANDARD DEVIAITON OF 1.8 YEARS, FIND THE PERCENT OF MOTORS THAT CAN BE EXPECTED TO REQUIRE REPAIR OR REPLACEMENT UNDER WARRANTY.

Answer 1

warranty of 8

mean of 10.2

the standard deviation is 1.8

10.2 - 8 = 2.2

2.2/1.8 = 1.22

the z score is -1.22

within 1.22 standard deviations is 38.8768%, so

38.8768 * 2 = 77.7536, 100 - 77.7536 = 22.2464, 22.2464 / 2 = 11.1232

11.1232%