The class mark of the class interval 10-25 is:
A12.5
B15
C17.5
D20
Answer & Solution
Correct answer: C. 17.5
1. A class interval is treated as if it were centred on its mid-point.
2. The mid-point of a class, also called its class mark, is the average of its upper and lower limits.
3. Here that is (10 + 25) / 2.
4. So the class mark is 17.5.
5. 15 is the width of the class, not its centre, which is the usual slip.
_Source: NCERT Class 10 Maths, Ch 13 'Statistics', S13.2 Mean of Grouped Data_
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