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?)

What is the chance that your cartridge can print less than8,763 pages (you are extremely unlucky)?That means in Math: P(X < 8,763) ?

Four decimals in this case.