The manufacturer of a laser printer reports the mean number
The manufacturer of a laser printer reports the mean number of pages a cartridge will print before it needs replacing is 12,225. The distribution of pages printed per cartridge closely follows the normal probability distribution and the standard deviation is 795 pages. The manufacturer wants to provide guidelines to potential customers as to how long they can expect a cartridge to last.
| The manufacturer of a laser printer reports the mean number of pages a cartridge will print before it needs replacing is 12,225. The distribution of pages printed per cartridge closely follows the normal probability distribution and the standard deviation is 795 pages. The manufacturer wants to provide guidelines to potential customers as to how long they can expect a cartridge to last. | 
Solution
mu = 12225
X = pages printed per cartridge is Normal (12225, 795)
E(X) = 12225
The cartridge will last 99% from mu-3sigma to mu+3 sigma
= (12225-3(795),12225+3(795))
= (9840, 14610)

