2.Suppose the life of a particular brand of calculator battery is approximately normally distributed with a mean of 75 hours and a standard deviation of 9 hours. Complete parts a through c.

a. What is the probability that a single battery randomly selected from the population will have a life between 65 and 85 hours?

P(65 overbar x85)=

(Round to four decimal places asneeded.)

b. What is the probability that 4 randomly sampled batteries from the population will have a sample mean life of between 65 and 85 hours?

P(65 overbar x85)=

(Round to four decimal places asneeded.)

c. If the manufacturer of the battery is able to reduce the standard deviation of battery life from 9 to 7 hours, what would be the probability that 4 batteries randomly sampled from the population will have a sample mean life of between 65 and 85 hours?

P(65 overbar x85)=

(Round to four decimal places asneeded.)