Writing Variable Expressions

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.

Rules

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”.
Multiplication: “”multiplied”, “times”, “double”, “triple”, “product”.
Division: “divide”, “split equally”, “distribute equally”.
Write an expression that includes the known numbers, a letter (x) in place of the unknown number, and the operation being used.

Example

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

Solution

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

Practice Writing Variable Expressions

Practice Problem 1

Write the phrase as a number.
7 feet under the water.

Practice Problem 2

Write the phrase as an algebraic expression.
$5 less than the current salary.
Let x = current salary.

Practice Problem 3

Fred has 17 dollars. Simon has x fewer dollars than Fred. Select the expression that shows the amount of money Simon has.

If Simon has 5 fewer dollars than Fred, how many dollars does Simon have?

Practice Problem 4

Alison bought x apples and combined them with 12 Eva’s apples. She then split them equally between 4 friends.
Write an expression that represents the number of apples that Alison shared among her friends.