Question

Rahul's father is three times as old as Rahul. Four years ago, his father was 4 times as old ​as Rahul. Four years ago, his father was 4 times as old as Rahul. How old is Rahul?

Answer 1

$$\begin{gathered} \mathrm{Let}\mathrm{the}\mathrm{present}\mathrm{age}\mathrm{of}\mathrm{Rahul}=\mathrm{x}\mathrm{yrs} \\ \mathrm{Then}\mathrm{age}\mathrm{of}\mathrm{father}=3\mathrm{x}\mathrm{yrs} \\ \mathbf{FOUR}\mathbf{}\mathbf{YEARS}\mathbf{}\mathbf{AGO}\mathbf{}\mathbf{:} \\ \mathrm{Rahul}\text{'}\mathrm{s}\mathrm{age}=\left(\mathrm{x}-4\right)\mathrm{yrs} \\ \mathrm{father}\text{'}\mathrm{s}\mathrm{age}=\left(3\mathrm{x}-4\right)\mathrm{yrs} \\ \mathrm{Now},\mathrm{according}\mathrm{to}\mathrm{question}: \\ 3\mathrm{x}-4=4\left(\mathrm{x}-4\right) \\ \Rightarrow 3\mathrm{x}-4=4\mathrm{x}-16 \\ \Rightarrow 3\mathrm{x}-4\mathrm{x}=-16+4 \\ \Rightarrow -\mathrm{x}=-12 \\ \Rightarrow \mathrm{x}=12 \\ \mathrm{So},\mathrm{present}\mathrm{age}\mathrm{of}\mathrm{Rahul}=12\mathrm{yrs} \end{gathered}$$