A "bell curve" is the common name of a Gaussian Probability Distribution,
because is is shaped like a bell. In a large class with a fair exam, the
marks will roughly follow a Gaussian Probability Distribution. An example
is shown to the right, for a class of 100 students and an exam marked out
of 10. The average mark is 7 out of 10.


When a professor crafts an exam, the objective is to have a fair
distribution of marks which is roughly Gaussian. However, it doesn't
always work out that way. If the exam is too hard, the marks distribution
might look more like this example shown to the right. The average mark is
only 3 out of 10.


Sometimes a professor makes an exam too easy. In which case the
marks distribution might look like this example shown to the right. The
distribution is no longer even Gaussian. These problems are compensated for, by what is commonly referred to as "curving the marks." For more information about how this is done, see the CLAW FAQ  How are the marks curved?

