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Question
The mean marks of 20 students is 62. It was later discovered that one of the students marks were written wrongly as 86 instead of 68. Find the correct mean.
Sum
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Solution
The mean marks of 20 students is 62
Total marks of all students (incorrect) = mean × number of students
= 62 × 20
= 1240
The incorrect mark for one student was 86, but the correct mark is 68. The difference between the incorrect and correct marks is
86 − 68 = 18
Correct total marks = 1240 − 18
= 1222
Correct mean = `"Correct total marks"/"Number of students"`
= `(1222)/20`
= 61.1
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