statistics
posted by Jessie .
Let X be a continuous random variable that is normally distributed with mean, µ = 15 and standard deviation, σ = 2.8, find a value xo that represents the 80th percentile of the distribution.

Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the Z score related to that proportion, then insert the values into the equation above and solve for the score.