## 26. Brother and Sister

- Sister, you have as many brothers as sisters.
- Brother, you have twice as many sisters as brothers.

Could you determine the number of children in this family from this conversation?
26. Let $x$ be the number of boys, and $y$ be the number of girls. The brother's words mean that

$$
x=y-1 \text {. }
$$

The sister's response can be written as the following equation:

$$
y=2(x-1), \text { or } y=2 x-2
$$

Substituting $x$ with $y-1$, we find that

$$
y=4
$$

and, consequently,

$$
x=3 \text {. } \quad .
$$

Thus, in this family, there are seven children: three boys and four girls.