The average marks obtained by a class in an examination were calculated as…
2025
The average marks obtained by a class in an examination were calculated as 30.8. However, while checking the marks entered, the teacher found that the marks of one student were entered incorrectly as 24 instead of 42. After correcting the marks, the average becomes 31.4. How many students does the class have?
- A.
25
- B.
28
- C.
30
- D.
32
Attempted by 21 students.
Show answer & explanation
Correct answer: C
Key idea: The correction changes the total marks by the difference between the correct and incorrect entries, and the change in average equals that change in total divided by the number of students.
Compute the increase in total marks: 42 - 24 = 18.
Compute the increase in average: 31.4 - 30.8 = 0.6.
Let n be the number of students. The increase in average equals the increase in total divided by n, so 18 / n = 0.6.
Solve for n: n = 18 / 0.6 = 30.
Conclusion: The class has 30 students.
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