UPSC 2015 CDS II Math Paper

Let the present ages of A, B and C be a, b and c years, respectively
∴a+b+c=24×3=72...(1)
Sum of ages of A and B four years ago=(a−4)+(b−4)
=18×2
=36
∴a+b=36+8=44....(2)
From (1) and (2), we have
c=72−44=28
Present age of C
= 28 years
Therefore, after 8 years, age of C=28+8
= 36 years