Use z-scores:
z = (91 - 86)/5 = ?
Once you calculate the z-score, check a z-table for the probability. (Remember that the problem is asking what is the probability the score was 91 or higher.)
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
1 answer