The life of a certain battery averages 10 hours with a stand

The life of a certain battery averages 10 hours with a standard deviation of 1.4 hours. What is the probability that a randomly selected bulb lasts:

a. from 9 to 11 hours? Explain what this probability tells you.

b. from 8 to 12 hours? Explain what this probability tells you.

c. from 7 to 13 hours? Explain what this probability tells you.

d. from 6 to 14 hours? Explain what this probability tells you.

Look at your answers a to d. Use a sketch of the normal curve to show what happened. What happens as the interval increases in size? Explain why. Is the increase in probability linear? Why?

Solution