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Mean of marks of a class, having 40 students, in a subject are 70. If marks of a student were mistakenly read as 87 instead of 78, then what is the ac

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Mean of marks of a class, having 40 students, in a subject are 70. If marks of a student were mistakenly read as 87 instead of 78, then what is the actual mean marks?
1. 69.775
2. 69.755
3. 70.757
4. 70.575
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Correct Answer - Option 1 : 69.775

Calculation:

Incorrect Mean = 70

Let the sum of the marks of the rest of the students be x

Incorrect Mean = 70

\(\rm x + 87\over40\) = 70

x + 87 = 2800

x = 2713

Correct sum = x + correct marks

S = 2713 + 78 = 2791

Correct Mean = \(\rm 2791\over40\) = 69.775

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