Let’s say son’s age = S Dad’s age = D 4 years ago, the son was (S-4) and dad now is three times that so D=3(S-4) Expand that to get D=3S-12
In 12 years, the son will be (S + 12) Dad will also be (D + 12) and he will be two times the sons age at that point so: D + 12 = 2(S + 12) Expand the right side: D +12 = 2S + 24 Subtract 12 from both sides: D = 2S + 12 So now D = 2S + 12 AND D = 3S - 12 Since both equations equal “D”, they must then equal each other: 2S + 12 = 3S - 12 Do some algebra and you get S = 24 Plug this back into EITHER “D=“ equations to find D D=2(24) +12 D=60
