STATS
posted by RACHELLE .
recent 10K run the finisher are norm dist with a mean of 55 min and stand dev of 13
A) determine the percentage of finishers with times between 45 and 75 min
B) determine the percentage of finshers less than 80 min
C) obtain the 30th percentile
D) find the 8th decile

Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores.
Reverse the process for the last 2 problems.
30th percentile = lowest 30%
8th decile = lowest 80%