Please help! What is the formula? And how should I plug in the numbers?

The number of pages printed before replacing the cartridge in a laser printer is normally distributed with a mean of 11,500 pages and a standard deviation of 800 pages. A new cartridge has just been installed.

What is the probability that the printer produces more than 12,000 pages before this printer must be replaced?

What is the probability that the printer produces fewer than 10,000 pages?

Thank you in advance.

Julius N2013-05-09T17:00:43Z

Favorite Answer

z = ( x - μ ) / σ
P (12000 < x) = P (0.625 < z) = 0.266
P (x < 10000) = P (z < -1.875) = 0.0304