A teacher prepares the following grouped frequency distribution of marks obtained by students in a unit test:
Marks (class interval): 20–30, 30–40, 40–50
Answer the following questions on the basis of the above information.
(i) Define (a) class size and (b) class mark.
(ii) Calculate the class size and the class mark for each of the three class intervals.
(iii) Explain whether these class intervals are suitable for drawing a histogram and give one reason for your answer.