posted by michelle .
The reaction time of subjects to a certain psychological experiment is considered to be normally distributed with a mean of 20 seconds and a standard deviation of 4 seconds. What is the reaction time such that only 10% of subjects are faster?
Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion (.10) related to the Z score. Insert Z score in equation above and solve for the score.