# Percentile from z-score

I have this question which i am so confused how to solve it

this is on normal curve. The following table is used to determine the student’s grades:

Grade       Z-score
A above     1.5
B           0.5-1.5
C           -0.5 to 0.5
D           -1.5 to -0.5
F           Below-1.5


Using this system, what percent of As Bs, Cs Ds and Fs are expected with a normal distribution of scores?

Now, I know the distribution is distributed in -2.1% - 13.4% - 34.1% (on both sides). It would have been easier if i could imagine that mean is 0 and sd is 1. but the above distribution doesn't match if i assume SD is 1 since the gap between 0.5 is 1 and then its 1 and so on (not sure if i am making any sense, I am just trying to think).

I am unable to put a finger how to go about this problem.

Thanks

• Z scores do have mean 0 and sd 1. Are you using tables? – Glen_b Sep 20 '16 at 4:20