An accelerated life test on a large number of type-D alkaline batteries revealed that the mean life for a particular use before they failed is 19.0 hours. The distribution of the lives approximated a normal distribution. The standard deviation of the distribution was 1.2 hours. About 95.44 percent of the batteries failed between what two values?
A) 8.9 and 18.9
B) 12.2 and 14.2
C) 14.1 and 22.1
D) 16.6 and 21.4

Question

Quizplus · Accepted Answer

95.44% corresponds to approximately two standard deviations from the mean in a normal distribution. The mean is 19.0 hours, and the standard deviation is 1.2 hours. Therefore, the range is 19.0 ± 2(1.2), which is 16.6 to 21.4 hours.

An Accelerated Life Test on a Large Number of Type-D