5623. A sample from a large batch of electric lamps contains 100 lamps. The average lamp life of the sampled lamps was found to be 1100 hours. Find an approximate 0.72 confidence interval for the average lamp life of the entire batch if the standard deviation of the lamp life of the batch is known to be 44 hours.

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)