Multiple choice

The average marks of 18 students in an examination was 60. It was later found that the marks of one student had been wrongly entered as 63 instead of 36. The correct average is:

  1. 59

  2. 59.5

  3. 58

  4. 58.5
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D Correct answer
Explanation

Sum of marks = 18 * 60 = 1080. Error: 63 instead of 36. Difference = 63 - 36 = 27. Correct sum = 1080 - 27 = 1053. Correct average = 1053 / 18 = 58.5.

AI explanation

The total reduction in the sum of marks is 63 minus 36, which equals 27. Using the average correction method, divide this total reduction of 27 by the total number of students, 18, to get a decrease of 1.5. Subtracting 1.5 from the initial incorrect average of 60 gives the correct average of 58.5.

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