Class mark
- CBSE · NCERT Class 10, Ch 13 Statistics
The class mark is the middle value of a class interval, found by adding its lower and upper limits and halving the total.
In grouped data, you know how many values fall in each class, but not the values themselves. So each class is treated as if all its values sit at its middle. That middle is the class mark. For the class 10-20, it is (10 + 20) ÷ 2 = 15. The class marks become the x values in the mean.
A small example
Three classes 0-10, 10-20 and 20-30 have frequencies 2, 3 and 5. Their class marks are 5, 15 and 25. Multiply each by its frequency: 10, 45 and 125. These add to 180, and the frequencies add to 10. So the mean is 180 ÷ 10 = 18.
Where marks go
Question 38 of CBSE's 2026-27 Maths Standard sample paper is a case study on Class X test scores, grouped into five class intervals. Part (iii)(A) asks for the mean, for 2 marks. The 2026-27 Maths Standard marking scheme gives 1 mark for a correct table. The table lists the class marks and each frequency times its class mark. The mean, 31.2, earns the other 1 mark.
Half the marks sit in the table, a clear case of step marking. A wrong class mark changes every product after it. The assumed mean method uses the same class marks, with smaller numbers.
Sources
Facts last checked against these sources on 30 September 2026.
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