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The average marks of 50 students in a class are 68. It is found that marks of two students were misread as 83 and 64 instead of 38 and 94 respectively. Find the actual average marks of the class. 
1. 68.3
2. 71
3. 66.6
4. 67.7

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Correct Answer - Option 4 : 67.7

Given:

Actual average marks of the 50 students = 68

The incorrect marks = 83 and 64

The correct marks = 38 and 94

Formula Used:

Average = Sum of all the observations/Total number of observations

Calculation:

Initial total marks = 50 × 68 = 3400

Difference between the correct and the incorrect marks = (38 - 83) + (94 - 64)

⇒ -45 + 30 = -15

Hence, the actual total marks = 3400 – 15 = 3385

Also, the actual average marks = 3385/50 = 67.7

∴ The correct average marks is 67.7

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