X+Y+Z = 24*3 = 72 X:Y = 2:3 (Given)
Let ?X? to be 2a & ?Y? to be 3a
X+Y = 60 (Given)
2a+3a = 60
5a = 60
a = 12
Hence, X = 24 & Y = 36
From equation (1)...
Z = 72 - 60
Z = 12
Hence, X - Z = 24-12 = 12.
Total sum of age of 80 students of the class = 15 X 80 = 1200 years
15 students ? 15 X 16 = 240 years
25 students ? 25 X 14 = 350 years
Sum of 40 students = 590 years
Total age of remaining 40 students = 1200 ? 590 = 610
So, average age = 15.25 years
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