statistics
posted by kelly .
The mean scale score on the mathematics examinatin of ninth graders in Texas was 86 with a standard deviation of 5 points. Given a student was selected at random what is the probability that his score was 91 or higher

Use zscores:
z = (91  86)/5 = ?
Once you calculate the zscore, check a ztable for the probability. (Remember that the problem is asking what is the probability the score was 91 or higher.)