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The average marks of a class of 35 children is 35. The marks of one student, who scored 35, were incorrectly entered as 65. What is the correct average of the class?

1. 34.14
2. 28.20
3. 42.21
4. 38.14

Correct answer: 34.14

Solution

The entered mark 65 should have been 35, so the total was overstated by 30. The incorrect total is 35 × 35 = 1225, so the correct total is 1225 − 30 = 1195. Dividing by 35 gives the correct average.

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