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