Question

Your friend has a z-table, and you don't. You ask your friend to look up the area in a tail on the left hand side of the normal distribution. Of the following answers that your friend might give you, only one of them even could be a correct proportion in a left-hand tail. Which one is it?

a. 0.8413
b. -0.3413
c. 0.5000
d. 0.4013

Answer 1

d. 0.4013

Explanation:

Half of the area under the normal curve is found to the left of the midpoint, where z=0. For negative values of z, the area under the curve is less than half.

Area under a normal curve is always a positive value between 0 and 1, so will never be negative.

The only value that can be an area in a left-hand tail is 0.4013.

_____

Additional comment

That value corresponds to z ≈ -0.25.