(i) The lower limit of the class 50−60 is 50.
(ii) Class mark for the class 40−50:
240 + 50​ = 290​ = 45
Again, class mark for the class 50 − 60:
250 + 60​ = 2110​ = 55
(iii) Here the class size is 40− 30, i.e. 10.