Question

The quality control manager at a light-bulb factory needs to estimate the mean life of a new type of light-bulb. The population standard deviation is assumed to be 50 hours. A random sample of 35 light-bulbs shows a sample mean life of 490 hours. Construct and explain a 90% confidence interval estimate of the population mean life of the new light-bulb.

For problem #1 above, what size sample would be needed to achieve a margin of error of 15 hours or less?

Answer 1