statics
posted by john .
The times for completing one circuit of a bicycle course are normally distributed with a mean of 81.7 minutes and a standard deviation of 8.6 minutes. An association wants to sponsor a race and provide prizes for the top (that is, fastest) 15% of riders. Where should they expect to set the cutoff time to earn a prize?

Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion (.15) that correspond to a Z score. Insert Z score and other values into the above equation and solve for the score.