# How do you solve x + y = 12 and y = 2x?

Oct 15, 2015

You can solve it like this:

#### Explanation:

We have 2 simultaneous equations:

$x + y = 12 \text{ } \textcolor{red}{\left(1\right)}$

$y = 2 x \text{ } \textcolor{red}{\left(2\right)}$

From $\textcolor{red}{\left(1\right)}$ we can write:

$y = \left(12 - x\right)$

Substituting this value of $y$ into $\textcolor{red}{\left(2\right)}$ gives:

$\left(12 - x\right) = 2 x$

$12 = 3 x$

$x = \frac{12}{3} = 4$

Substituting this value of $x$ into $\textcolor{red}{\left(1\right)}$ gives:

$4 + y = 12$

$y = 12 - 4$

$y = 8$