UPSC Prelims 2019·CSAT·Quantitative Aptitude·Arithmetic

The average marks of 100 students are given to be 40. It was found later that marks of one student were 53 which were misread as 83. The corrected mean marks are

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Last updated 23 May 2026, 3:31 pm IST
  1. A39
  2. B39.7Correct
  3. C40
  4. D40.3

Explanation

The initial total marks for 100 students were 100 * 40 = 4000. One student's marks were 53 but misread as 83. This means 83 - 53 = 30 marks were incorrectly added to the total. To correct the total marks, we subtract this excess: 4000 - 30 = 3970. The corrected mean marks are the corrected total divided by the number of students: 3970 / 100 = 39.7. Analyzing the options: A) 39: This would imply a larger error correction, which is incorrect. B) 39.7: This is the correct calculation based on adjusting the total marks. C) 40: This is the original incorrect mean, implying no correction was made. D) 40.3: This would result if the error was added to the total instead of subtracted, or if the error was -30 instead of +30.
Quantitative Aptitude: The average marks of 100 students are given to be 40. It was found later that marks of one student were 53 which were mi
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