# Question #b6c11

Oct 18, 2017

See a solution process below{

#### Explanation:

Let's call the age of the younger sister: $a$

Then, the age of the older sister is: $2 a$

If the sum of their ages is $12$ we can write this equation and solve for $a$:

$a + 2 a = 12$

$1 a + 2 a = 12$

$\left(1 + 2\right) a = 12$

$3 a = 12$

$\frac{3 a}{\textcolor{red}{3}} = \frac{12}{\textcolor{red}{3}}$

$\frac{\textcolor{red}{\cancel{\textcolor{b l a c k}{3}}} a}{\cancel{\textcolor{red}{3}}} = 4$

$a = 4$

The younger sister is: 4 years old.

The older sister is: $2 \times 4 =$8 years old.