Question 152042
An sd of 0 means there is no 'spread' around the mean, So everyone got the same grade

The class with 91 and a small s, tells us the the grades are spread normally and tightly around a mean of 91. So the class did well and everyone got a great grade.

The class with an 85 mean and an sd of 20 tells us the grades are widely spread. Some students did really well; others did not.