Expressions and Equations / What is a Variable?

Understanding

Algebraic expressions specify numerical calculations using numbers and letters or symbols standing for numbers.

What to look for

Students leave behind the symbol “x” for multiplication and come to understand that the juxtaposition of a number and a variable such as 3x implies multiplication between 3 and x.

Sample Assessment

If a=115 and b=45, what would be the value of the expression b+(a - b)?

a 115  b. 185  c. 205  d. 275

Answer: a. 115

The Big Idea

A variable might stand for a range of numbers that can be used in a mathematical expression; a variable might be used in a universal statement that is true for all numbers; or a variable might stand for a specific value such as the solution to an equation or word problem.

What are the students doing?

Students evaluate expressions, write expressions that correspond to given situations, and use expressions and formulas to solve problems.

What is the teacher doing?

You might want to point out that any letter could be used in the expressions; the files just happen to use x.