Question

Sindhu is $40$ years old and Smita is $20$ years old. How many years ago was Sindhu three times as old as Smita?

Answer 1

Let $x$ years ago, Sindhu was three times as old as Smita,

So, $x$ years ago

Sindhu's age was $40-x$ and Smita's age was $20-x$.

Now, according to the given condition, we have

$$\begin{gathered} 40-x=3\left(20-x\right) \\ 40-x=60-3x \\ 40-x-60+3x=0 \\ -20+2x=0 \\ 2x=20 \\ x=\frac{20}{2} \\ x=10 \end{gathered}$$

Hence, Smita was $3$ times of Sindhu’s age before $10$ years.