## B.2 When the $$z$$-score is known, and the area is sought

The table gives the probability (area) that a $$z$$-score is less than the $$z$$-score looked up. For example: Look up $$z = -1.87$$; the area less than $$z = -1.87$$ is about 0.0307, or about 3.1%.

To use this table, enter the $$z$$-score in the search box under the z.score column. The area will be shown. The table includes $$z$$-values between -4 and 4. (Alternatively, you can search through the table manually.)

The online Tables work with two decimal places. As an example, then, consider finding the area to the left of $$z=-2.00$$. In the tables, the value -2 is entered in the search region, just under the column labelled z.score (see the animation below). After pressing Enter, the answer is shown in the column headed Area.to.left: the probability of finding a $$z$$-score less than $$-2$$ is 0.0228, or about 2.28%.

The hard-copy tables work differently. On the tables, look for $$-2.0$$ in the left margin of the table, and for the second decimal place (in this case, 0) in the top margin of the table (see the animation below): where these intersect is the area (or probability) less than this $$z$$-score. So the probability of finding a $$z$$-score less than $$-2$$ is 0.0228, or about 2.28%.