A father puts money into savings accounts for his sons every year. He does this on the same date every year. And he uses the same formula to determine how much money each boy gets - a very simple formula.
He puts into each boy's account £10 for every year old that son was on his most recent birthday.
This year he put into Andrew's account one and a half times as much as he put into Brian's account.
Four years ago Andrew received as much money as Brian and Charles put together.
And four years before that Brian got exactly quarter of the money that was given to the three sons.
How old are the three boys now?
From the first fact we get A = 3B / 2 
From the second fact we get A - 4 = B - 4 + C - 4 which gives
A = B + C - 4 
And from the third fact we get 3(B - 8) = A - 8 + C - 8 which gives
3B = A + C + 8 
If we put  into  we get 3B / 2 = B + C - 4 which gives
B = 2C - 8 
And putting  into  we get 3B = 3B / 2 + C + 8 which gives
3B = 2C + 16 
Subtracting  from  we get 2B = 24 and thus B = 12.
Putting B = 12 into  we get 12 = 2C - 8 and so C = 10.
And putting B = 12 into  we get A = 36 / 2 and so A = 18.
So Andrew is 18, Brian is 12 and Charles is 10.