The Frequency Distribution of Lifetimes of a Tiny Battery to Power

Short Answer

The frequency distribution of lifetimes of a tiny battery to power hand calculators is normal with

and

. Out of every 1000 batteries produced, how many would we expect to last:
(a)over 600 hours?
(b)less than 550 hours?
(c)between 500 and 550 hours?
(d)between 550 and 600 hours?
(e)over 650 hours?