# Mary, who is sixteen years old, is four times as old as her brother. How old will Mary be when she she is twice as old as her brother?

Dec 2, 2016

$24$ years old

#### Explanation:

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

Let $x$ be the year when Mary will be twice as old as her brother.

$16 + x = 2 \left(4 + x\right)$

$x = 8$

Therefore, Mary will be

$16 + 8 = \text{24 years old}$

while her brother will be

$4 + 8 = \text{12 years old}$