We can represent sums, differences, products, and quotients of rational numbers, and combinations of these, with numerical and algebraic expressions.

Sums:

$\frac12 + (\text-9)$

$\text-8.5 + x$

Differences:

$\frac12 - (\text-9)$

$\text-8.5 - x$

Products:

$(\frac12)(\text-9)$

$\text-8.5x$

Quotients:

$(\frac12)\div(\text-9)$

$\frac{\text-8.5}{x}$

We can write the product of two numbers in different ways.

- By putting a little dot between the factors, like this: $\text-8.5\boldcdot x$.
- By putting the factors next to each other without any symbol between them at all, like this: $\text-8.5x$.

We can write the quotient of two numbers in different ways as well.

- By writing the division symbol between the numbers, like this: ${\text-8.5}\div{x}$.
- By writing a fraction bar between the numbers like this: $\frac{\text-8.5}{x}$.

When we have an algebraic expression like $\frac{\text-8.5}{x}$ and are given a value for the variable, we can find the value of the expression. For example, if $x$ is 2, then the value of the expression is -4.25, because $\text-8.5 \div 2 = \text-4.25$.