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Mathematics » Introducing Integers » Subtract Integers

# Evaluating Variable Expressions with Integers

This is a lesson from the tutorial, Introducing Integers and we encourage you to log in or register before you continue, so that you can track your progress.

## Evaluating Variable Expressions with Integers

Now we’ll practice evaluating expressions that involve subtracting negative numbers as well as positive numbers.

## Example

Evaluate $$x-4\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}$$

1. $$\phantom{\rule{0.2em}{0ex}}x=3\phantom{\rule{0.2em}{0ex}}$$
2. $$\phantom{\rule{0.2em}{0ex}}x=-6.$$

### Solution

To evaluate $$x-4$$ when $$x=3$$, substitute $$3$$ for $$x$$ in the expression.

 Subtract.

To evaluate $$x-4$$ when $$x=-6,$$ substitute $$-6$$ for $$x$$ in the expression.

 Subtract.

## Example

Evaluate $$20-z\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}$$

1. $$\phantom{\rule{0.2em}{0ex}}z=12\phantom{\rule{0.2em}{0ex}}$$
2. $$\phantom{\rule{0.2em}{0ex}}z=-12$$

### Solution

To evaluate $$20-z\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}z=12,$$ substitute $$12$$ for $$z$$ in the expression.

 Subtract.

To evaluate $$20-z\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}z=-12,\phantom{\rule{0.2em}{0ex}}\text{substitute}\phantom{\rule{0.2em}{0ex}}-12\phantom{\rule{0.2em}{0ex}}\text{for}\phantom{\rule{0.2em}{0ex}}z\phantom{\rule{0.2em}{0ex}}\text{in the expression.}$$

 Subtract.