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The average marks of 18 students in an examination were 60. It was later found that the marks of one student had been wrongly entered as 63 instead of 36. The correct average is:
- A59
- B59.5
- C58
- D58.5
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CCommunity
Trick:
⇒ Difference in the mark = 36 - 63 = -27
⇒ Reduction in average per student = Difference/number of students = -27/18 = -1.5
∴ New average = 60 - 1.5 = 58.5
Detailed solution:
⇒ Wrongly calculated total of class = average × number of students = 60 × 18 = 1080
⇒ Original total = 1080 - 63 + 36 = 1053
∴ New average = 1053/18 = 58.5
⇒ Difference in the mark = 36 - 63 = -27
⇒ Reduction in average per student = Difference/number of students = -27/18 = -1.5
∴ New average = 60 - 1.5 = 58.5
Detailed solution:
⇒ Wrongly calculated total of class = average × number of students = 60 × 18 = 1080
⇒ Original total = 1080 - 63 + 36 = 1053
∴ New average = 1053/18 = 58.5