Question 331524
let age of sons be x & y & father's age =z
z = 3(x+y)
z/3 = (x+y)
..
after 5 years
their ages will be
x+5, y+5, z+5
z+5=2(x+5+y+5)
z+5=2x+2y+20
z+5=2(x+y)+20
z+5-20=2(x+y)+20-20
z-15=2(x+y)
But (x+y)= z/3
z-15=2*z/3
multiply 3
3*(z-15)=2z
3z-45=2z
3z-2z=45
z=45  father's age