Question: As part of their quality assurance program, the Shakespeare Battery Company of Stratford upon Avon conducts tests on battery life. For a particular D cell alkaline battery, the mean life is 19 hours. The useful life of the battery follows a normal distribution with a standard deviation of 1 .2 hours.

Answer the following questions.

(a) About 68 percent of the batteries failed between what two values?

(b) About 95 percent of the batteries failed between what two values?

(c) Virtually all of the batteries failed between what two values?