Assume the printer cartridges in 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 cartridger can print between 10,400 9,999 to 11,200 10, 969 pages? That means in Math: P(9,999 < X < 10,969) = ?

4 decimals