Computer Sciences > GATE 2025 SET-1 > Average
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?
Correct : c
Explanation:
1. Identify the Change in Total Marks: The student's marks were mistakenly entered as 24 instead of 42.
Difference = Correct Marks - Incorrect Marks
Difference = 42 - 24 = 18 marks
• This means the total sum of marks for the class must increase by 18 after correction.
2. Identify the Change in Average Marks:
Increase in Average = New Average - Old Average
Increase in Average = 31.4 - 30.8 = 0.6
3. Calculate the Total Number of Students: Let the total number of students in the class be N.
Increase in Total Marks = N × Increase in Average
18 = N × 0.6
N = 18 / 0.6 = 30
4. Conclusion: The class has exactly 30 students.
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