Question
In an examination, the average marks obtained by the
students is 85. After correcting the quantitative mistakes, the average of 100 students is reduced to 70 from 85 and the overall average of the student is reduced to 80. Then find the total number of students who participated in that examination?Solution
Let the total number of students be x Average marks obtained by the students = 85 Total marks = 85x After correcting the quantitative mistakes the average decreased by (85 - 70) = 15 marks Total reduction = 15 × 100 = 1500 Now According to the Question, (85x - 1500)/x = 80 80x = 85x – 1500 x = 300 Total number of students = 300
Alternate method: By alligation method, 
Total number of students = 200+100 = 300
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