given x is a noramlly distributed random variable with a mean of 28 and a sd of 7 find p(x<28)
Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to the Z score.
However, since mean = 28, and in a normal distribution, the mean = median, and the median = 50th percentile, you would have your answer.