CJ Computer Disks stocks and sells recordable CDs. The monthly demand for these CDs is closely approximated by a normal distribution with a mean of 20,000 disks and standard deviation of 4,000 disks. CJ receives shipments from the supplier once per month (at the beginning of each month).
a. Find the probability that the demand for recordable CDs exceeds 30,000 for a particular month.
b. Find the probability that the demand for recordable CDs is between 12,000 and 18,000.
c. How large an inventory must CJ have available at the beginning of the month so that the probability of running out of recordable CDs (a stock out) during the month is no more than .05?