Suppose we have a distribution We will find using the diagram on the left.

This corresponds to a probability of 0.6915 hence

Now we will find illustrated by the diagram on the left. Ignoring the minus sign we go to the normal distribution tables and look for the probability corresponding to finding 0.7422. Because we had a negative value ofwe subtract this from 1. We have found Because the probabilities in the tables are all of the form We subtract this value from 1 again to obtain

Now we use