Multiple choice

The average score of a class of 50 students was calculated to be 64.15. It was later discovered that the score of one student was incorrectly taken to be 39, instead of 75. Find the actual average score of the class.

  1. 64.53

  2. 64.87

  3. 64.95

  4. 65.01

  5. 65.12
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B Correct answer
Explanation

The original sum of scores was 50 * 64.15 = 3207.5. The error was subtracting 39 and not adding 75. The correction is (75 - 39) = 36. New sum = 3207.5 + 36 = 3243.5. New average = 3243.5 / 50 = 64.87.

AI explanation

Use the formula for average adjustment: change in average = (correct value - incorrect value) / total count. The difference between the correct and incorrect score is 75 - 39 = 36. Divide this difference by the total number of students: 36 / 50 = 0.72. Add this positive increment to the initially calculated average to get the actual average: 64.15 + 0.72 = 64.87.

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