A manufacturer of light bulbs claims that its light bulbs ha

A manufacturer of light bulbs claims that its light bulbs have a mean life of 690 hours and a standard deviation of 121 hours. You purchased 146 of these bulbs and decided that you would purchase more if the mean life of your current sample exceeded 679 hours. What is the probability that you will not buy again from this manufacturer? (Give your answer correct to four decimal places.)

Solution

Sample mean >679 probability is required

Mean difference = -11

Std error = 121/rt 146 = 10.01403

Z statistic = -1.098

prob for no buying= 1-0.8438

= 0.1562