1. Histograms of grades in two classes, each of 200 students
The standard deviation of the grades in one class is 8 and the other is 3.

2. Another class: mean grade is 75, standard deviation of grades is 4

4. Z-scores
To get a z-score for an observation: subtract the mean and divide the difference by the standard deviation.
The z-score gives the number of standard deviation units that the observation is away from the mean.
Z-scores are useful for comparing the relative position of observations from different distributions.