Question

A GE lightbulb is supposed to last for 1,200 hours. In fact, light bulbs of this type last only 1,185 hours with a standard deviation of 70 hours. What is the probability that a sample of 100 lightbulbs will have an average life of at least 1,200 hours? Mathematics

Answer 1

Answer: 0.0161

Miss Philadelphia was right about most of the answer, except she forgot to subtract 0.9839 from 1. 1 - 0.9839 = 0.0161, or 1.61%.

Answer 2

This can be solved using the formula for t test which is = x - mu over standard deviation divided by the square root of the number of samples. In this case, it is 1185 - 1200 over 70 divided by square root of 100 which give us a value of 2.14 which is equal to .9839 in area. Only rarely, just over one time in a hundred tries of 100 light bulbs, would the average life exceed 1200 hours.