Question

What is `"P"(Z< –2.31) + "P"(Z> 2.31)`?

Answer 1

The answer is 0.0208.

Explanation:

This one's easy; all you do is use a `z`-table. Look up the value in the table for `z="-"2.31`, then double it (since the standard normal curve is symmetrical about 0).

A `z`-table (like the one above) is used to find the area under the standard normal curve to the left of any given value for `z`. So, for example, the area to the left of -2.31 is the number in row -2.3 and column 0.01. Using the table above, we find that value to be 0.0104.

But wait—that's just the area of the left tail! The area under both tails is twice this amount (since the two tails are identical due to the symmetry of the standard normal curve). Thus, we double 0.0104 to 0.0208, and this is our final answer.