Question

Maintenance managers must decide when to change the light bulbs in streetlamps and other relatively inaccessible installations. It is costly to send out crews to change a single failed bulb. If each bulb lasts approximately the same amount of time, they can all be changed at once, producing significant cost savings. Suppose that a financial analysis of the lights at Coors field has concluded that it will pay to replace all of the light bulbs at the same time if the variance of the lives of the bulbs is less than 250 hours². The lengths of life of the last 100 bulbs were recorded, with the results shown below.

Mean lifetime = 1999.6 hours              Lifetime standard deviation = 25.5 hours

Using a 5% significance level, can we conclude that all bulbs should be replaced at the same time?

Answer 1