Standard Deviation?

A teacher gave a 25 multiple choice question test. After giving the tests, she computed a mean and standard deviation of the scores. The standard deviation was 0. Based on this info:


a) all the students had the same score


b) she must have made a mistake


c)about half the scores were above the mean.





please explain!

Standard Deviation?
Standard deviation provides the intervals for a standard bell curve, which would give you the percent of people which got a certain score.





If the intervals on the bell curve were 0, all students would have the same score. Because of that, half of the scores could not be above the mean, since they all are the mean score, and while it is possible a mistake was made, all students getting the same score would be the correct answer
Reply:A, but probably B. If the SD was zero, the teacher could just look at the scores and know that!
Reply:SD = 0 is possible only if all the scores are the same. So, a is correct (although quite possibly b is also correct :) )

wallflower