Jessica Salas, President of Salas Products, is reviewing the warranty policy for her company's new model of automobile batteries.Life tests performed on a sample of 100 batteries indicated: (1)an average life of 75 months, (2)a standard deviation of 5 months, and (3)a bell-shaped battery life distribution.What percentage of the batteries will fail within the first 65 months of use?
A)0.5%
B)1%
C)2.5%
D)5%
E)7.5%

Question

Quizplus · Accepted Answer

Using the empirical rule (68-95-99.7 rule) for a normal distribution, approximately 95% of the data falls within two standard deviations from the mean. Here, 65 months is two standard deviations below the mean (75 - 2*5 = 65). Therefore, about 2.5% of the batteries will fail within the first 65 months.

Jessica Salas, President of Salas Products, Is Reviewing the Warranty