Evaluating Expressions ............................

When you know the value of a variable, you can replace the variable by that number and actually work out an answer for the expression.
This process is called evaluating an expression.

For example, consider the expression 3p + 1
This means 'three times a number, plus one'

If you know that the variable p is actually 5, you can work out the answer:

3p + 1 = 3(5) + 1 = 16

The variable p gets replaced by 5
When you do this, the expression works out to be 16

Here are two more examples of expressions being evaluated.

Evaluate 2w - 5 when w = 4

2w - 5

= 2(4) - 5

= 3

Evaluate 5x + 1 when x = 7

5x + 1

= 5(7) + 1

= 36

When evaluating an expression, you should show three steps:

the expression with a variable in it
the expression with the number replacing the variable
the answer after working it out

You are probably already familiar with some expressions and how they are evaluated. Some of them even have more than one variable. For example:

The area of a rectangle can be calculated if you know the length and width:

The expression for area is given by:

A = L · W where L and W are the variables.

In this example, we know that L = 6 and W = 5, so we can replace the variables with these values:

A = L · W = 6 · 5 = 30