DRDO Multi tasking staff Model paper 2

Let the total number of students be ‘x’
∴ Sum of the ages of all students = 14x
0.25x number of students have an average age of 12
∴ Sum of the ages of 25% students = 3x
0.4x number of students have an average age of 14
∴ Sum of the ages of 40% students = 5.6x
Sum of ages of (25% + 40% + rest of the students) = 14x
∴ 3x + 5.6x + Sum of the ages of the remaining 35% students = 14x
∴ Sum = 5.4x
∴ Their average age = 5.4x/(0.35x) = 15.4
∴ The average age of the remaining students is 15.4 years