The mean life of a particular brand of light bulb is 1200 hours and the standard deviation is 75 hours.Tests show that the life of the bulb is approximately normally distributed.It can be concluded that approximately 68% of the bulbs will last between _______.
A)900 and 1100 hours
B)950 and 1050 hours
C)975 and 1475 hours
D)1050 and 1350 hours
E)1125 and 1275 hours

Question

Quizplus · Accepted Answer

Approximately 68% of data in a normal distribution falls within one standard deviation of the mean. Here, the mean is 1200 hours and the standard deviation is 75 hours. Therefore, 68% of the bulbs will last between 1200 - 75 = 1125 hours and 1200 + 75 = 1275 hours.

The Mean Life of a Particular Brand of Light Bulb