Concept

To write variable expression means to create an algebraic expression that represents a verbal problem. A variable is a letter that stands for an unknown number in a mathematical expression.

Rule

When given a word problem, find vocabulary that shows what operation is being used.

Addition: “more than,” “plus,” “total,” “and”, “sum”.
Subtraction: “fewer”, “less than”, “taken away”, “difference”.

Write an expression that includes the known numbers, a letter (x) in place. of the unknown number, and the operation being used.

Example

Sara bikes 5 miles to work each day, plus another x miles after work. Select the expression that shows the number of miles Sara bikes each day. 

If Sara biked 12 miles after work today, how many miles did she bike in all?

Solution

Expression: 5 + x                  
Sara biked 17 miles in all.

Find the vocabulary that shows what operation is being used.
“Plus” means addition, so the correct expression is:

5 + x

If Sara biked another 12 miles after work, then Sara biked 5 + 12 miles.

The answer is: 17 miles

Prerequisite Skills

Evaluate Variable Expressions (5.6.2)

Write Expressions and Number Sentences (4.3.1)