When there are a lot of datas to analyse like the examples given, it's easier to classify the datas into groups for analysis.
The class limits are composed of the lower class limit and the upper class limit. Each class has a respective set of class limits.
When making a histogram, there should be no gaps between the bars. Therefore, the midpoints between the upper class limit of a class and the lower class limit of the next class in the sequence are calculated to be the class boundaries.
Class interval is the difference between two adjacent class boundaries.