The average marks of 40 students in an examination is 25. Later it is found that the marks of one student were wrongly entered as 73 instead of 37. What is the correct average marks for the class?

Introduction / Context:
This is another example of correcting an average when one observation has been entered incorrectly. It reinforces the method of adjusting the total sum first and then recomputing the mean.

Given Data / Assumptions:
- There are 40 students in the class.
- The initially reported average marks is 25.
- One student's marks were wrongly recorded as 73 instead of the correct value 37.
- We must find the corrected class average.

Concept / Approach:
As before, the average equals total marks divided by the number of students. We begin with the incorrect total implied by the wrong average, then adjust this total by removing the incorrect value and adding the correct one. Finally, we divide the corrected total by 40.

Step-by-Step Solution:
Step 1: Incorrect total marks = 25 * 40. Step 2: Compute 25 * 40 = 1000 marks. Step 3: The wrong entry is 73, the correct value is 37, so we must subtract 73 and add 37 to correct the total. Step 4: Correct total = 1000 - 73 + 37. Step 5: Compute 1000 - 73 = 927, then 927 + 37 = 964. Step 6: Correct average = 964 / 40. Step 7: 964 / 40 = 24.1 marks.

Verification / Alternative check:
The net error in the total is 73 - 37 = 36 marks too high. So we can also compute the corrected total as 1000 - 36 = 964 directly. Dividing 964 by 40 again gives 24.1, confirming the answer.

Why Other Options Are Wrong:
- Option 24.3: This would correspond to a total of 972 marks, which does not match the corrected sum 964.

- Option 24.5: This implies a total of 980 marks, again inconsistent.

- Option 24.7: This would imply 988 marks, which is too high given the nature of the correction.

Common Pitfalls:
Students sometimes try to average 25 and the corrected mark or directly adjust the average by the error divided by the number of students but with incorrect sign. The safe method is always to reconstruct the total, correct it, and then divide by the class strength.

Final Answer:
The correct average marks of the class is 24.1.