# Regne ut uttrykk med to variabler

We've already evaluated expressions with one variable. Now it's time to do it with two variables.

## How to evaluate an expression with two variables

Let's say we want to evaluate the expression $10 + 2p - 3r$. Well, first we need to know the values of $p$ and $r$. For example, to evaluate the expression when $\blueD {p = 4}$ and $\goldD{r = 5}$, we just replace $\blueD p$ with $\blueD 4$ and $\goldD r$ with $\goldD 5$:
$\phantom{=}10 + 2\blueD p - 3\goldD r$
$=10 + 2\cdot\blueD 4 - 3 \cdot \goldD5$
$=10 + 8 - 15$
$=3$
So, the expression $10 + 2p - 3r$ equals $3$ when $p = 4$ and $r = 5$.