How do I calculate the lower class boundary and the upper class boundary for the class 40 - 59?
It depends whether your variable is discrete or continuous .
A discrete variable can only have certain values, whole numbers in your case. Think of number of students in a certain course.
If this is the case the class goes from 40 to 59, and the class midpoint will be 49.5
A continuous variable can have any value.
Think of age, where "
In this case the upperboundary will be
A third case is when the values have been rounded , like exam scores. There
So it really does depend on the kind of data that you have.