Thirty six students of class IX contributed on an average ₹42 towards flood relief fund whereas some students of class X contributed on an average ₹54.50. If the overall average contribution per student remained ₹47, then how many students of class X contributed?

24

Average Donation made by 36 students of class IX = 42

Total Donation made by Class IX = 42*36

Average Donation made by 'S' students of class X = 54.5

Total Donation made by Class X = 54.5*S

Overall average contribution per student = 47

(Total contribution by Class IX + Total contribution by Class X)/(Number of Students of Class IX+ Number of Students of Class X) = 47

(42*36 + 54.5S)/(36+S) = 47

42*36 + 54.5S = 47S + 36*47

54.5S - 47S = 36*47 - 42*36 = 36*(47-42)

7.5S = 36*89 = 36*5

S= 180/7.5

The correct answer is Option (3) → 24