5614. Twenty-five lamps were taken to test the service life of electric lamps by random resampling. Their average life turned out to be 980 hours. Determine with a reliability of 0.9876 the boundaries of the confidence interval for the general average, assuming that the life of the lamps is distributed according to the normal law with a standard deviation of 20 hours.

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