The hemoglobin A1c test, a blood test given to diabetic's patients during their periodic checkups, indicates the level of control of blood sugar during the past 2 to 3 months. The following data values were obtained for 40 different diabetics patients at a university clinic:

Classify these A1c values into a grouped frequency distribution using the classes 3.7–4.7, 4.7–5.7, and so on.
What are the class midpoints for these classes?

It's the same as midpoint. Add the two class boundaries then divide by two.