Power+, produces AA batteries used in remote-controlled toy cars. The mean life of these batteries follows the normal probability distribution with a mean of 34 hours and a standard deviation of 4.8 hours. As a part of its testing program, Power+ tests samples of 36 batteries.

a. What proportion of the sample will have a mean useful life greater than 33.5 hours?

b. What proportion of the sample will have a mean useful life between 33.5 and 35 hours?