(BACKGROUND ONLY) The manager of a computer help desk operation has collected enough data to conclude that the distribution of time per call is normally distributed with a mean equal to 8.21 minutes and a standard deviation of 2.14 minutes. Based on this, what is the probability that a call will last longer than 13 minutes?

(I UNDERSTAND THIS)

The given information is, = 8.21 minutes and = 2.14 minutes.

P (call will last more than 13 minutes) = P (X>13), where x is a normal variate.

For x=13, the z-score as follows:

z=(x- )/ .

z= (13-8.21)/2.14 = 4.79/2.14= 2.2383.

Use the z- calculator or Standard-Normal chart,

Then the probability P (X>13) =P (z>2.2383)

= 0.0125. <------- ????

QUESTION: HOW DO I USE THE STANDARD-NORMAL CHART, TO CONVERT

P (X>13) =P (z>2.2383) = 0.0125?????

Would you please explain. step by step. thank you very much.