Assume the printercartridgesin average can print 12,000 pages with 800 pages as its standard deviation (= 12000, = 800), and it is a bell-shaped distribution for the number of pages (X) it can print before running of of ink.(X is a random variable, isn't it?)

To answer "What is the chance that your cartridge can print more than13,678 pages (it means that you are very very lucky to have a great cartridge)?That means in Math: Prob(X > 13,678) or in short: P(X > 13,678) = ? ", you need to first calculate the Z-value.

So what is the Z-value? Z = (X-)/, two decimals.