The class marks of a frequency distribution are 47, 52, 57, 62, 67, 72, 77. Determine the (i) class size (ii) class limits with respect to the class mark 52 (iii) true class limits for class mark 52.
Class marks of the given frequency distribution are = 47, 52, 57, 62, 67, 72, 77
(i) Class size = 52 – 47 = 5
(ii) Class size = 5
Mid value = 
= 2.5
Class marks = 52
Upper class limit = 52 + 2.5 = 54.5
Lower class limit = 52 – 2.5 = 49.5
(iii) Here classes are in the exclusive form,
So true class limit for class mark 52 is 49.5 – 54.5
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