Define class size.

Hint: For defining class size we need to be aware about some basics of statistics. We need to be aware about terms such as grouped data, class intervals. If we have a legitimate grouped data where each of the group has a defined number of points then we would be able to define the size of that class and as the term itself suggests, it tells the length of the class which will be obtained by subtracting the lower limit from the upper limit of any interval of the grouped data.

Complete step-by-step solution:
Suppose we have a grouped data which has a certain level of labels in each of the classes. For example, from 1 to 10, the frequency is 2. From 11 to 20, the frequency is 4 and so on. Such intervals are called classes and we get frequencies while we collect the data and we assign them to certain classes accordingly. We see that the frequency might vary but the length of the class is not varying at all. This defined length that does not change in the data is called the class size.
The class size is obtained by subtracting the lower limit of the class from the upper limit. For example, if the class interval is something like this$\left(0,10\right)$, then the class size is 10-0=10.

Note: Do not get confused between class size and class interval. The collection of all points that come in a class makes a class interval but if we just want to know the range of the points then we calculate the class size of the class.