Question Number 65951 by ketto2 last updated on 06/Aug/19
Commented by Tony Lin last updated on 06/Aug/19
$${if}\:{the}\:{son}\:{is}\:{x}\:{now}\: \\ $$$$\Rightarrow{his}\:{father}\:{is}\:\mathrm{30}+{x} \\ $$$${after}\:\mathrm{10}\:{years} \\ $$$$\Rightarrow\mathrm{40}+{x}=\mathrm{3}\left({x}+\mathrm{10}\right) \\ $$$$\Rightarrow{x}=\mathrm{5} \\ $$$${so}\:{the}\:{son}\:{is}\:\mathrm{5}\:{years}\:{old} \\ $$$${and}\:{his}\:{father}\:{is}\:\mathrm{35}\:{now} \\ $$