posted by Angie .
Dorian's score of 558 on the writing portion of the 2009 SAT exam placed him in the 72nd percentile. If the mean on this exam was 493, what was the standard deviation?
Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion (.72) and its Z score. Insert the Z score and other data in the equation above and solve for SD.