Question

Mary, who is sixteen years old, is four times as old as her brother.

How old will Mary be when she is twice as old as her brother?

Answer 1

Find the age of Mary and her brother :

When Mary is $16$, her brother is $4$.

Mary's chronological age difference from her brother's will be two in the year $\mathrm{x}$.

$$\begin{gathered} 16+\mathrm{x}=2(4+\mathrm{x}) \\ \mathrm{x}=8 \end{gathered}$$

Therefore, Mary will be $16+8=24$ years old

Although her brother will $4+8=12$ years old

Hence, Mary is $24$ years old and her brother is $12$ years old.