Math Background

Lesson: Expressions and Equations
Introducing the Concept

Without realizing it, your students simplified expressions and solved equations when they were asked to add and subtract given numbers. They probably didn't know that 5 + 3 is an expression and that 7 + 2 = 9 is an equation. It is important for students to understand these terms in order for them to clearly understand the similarities and differences between equations and expressions. They will begin to use algebraic expressions that feature variables as well. By employing their addition and subtraction skills, they will be simplifying expressions and evaluating algebraic expressions. Stress the progression from an expression to an equation by demonstrating how equal expressions are found on either side of an equals sign.

Materials: overhead projector or chalkboard

Preparation: none

Prerequisite Skills and Concepts: Students should have a working knowledge of addition and subtraction.

Write 5 + 3 and 5 + 3 = 8 on the board or overhead. Have a student read aloud the expression 5 + 3 and the equation 5 + 3 = 8.

  • Ask: What is the difference between 5 + 3 and 5 + 3 = 8?
    Many students will quickly respond by stating that one has an equals sign and the other does not.
  • Say: 5 + 3 is called an expression. An expression consists of a number or a combination of numbers joined by operation symbols. An expression does not have an equal sign.
    Erase 5 + 3. Point to 5 + 3 = 8.
  • Ask: What is on the left side of the equals sign? What is on the right side?
    Elicit from students that an expression or value is on both sides of the equals sign in 5 + 3 = 8. Try to have students describe the numbers as well as the operation. The left side is an expression, 5 + 3, that is equal to the value of the right side, 8.
  • Say: 5 + 3 = 8 is called an equation. The left side of an equation equals the right side.

    Continue with additional examples, using different numbers. Try using two numbers on each side as well. Make sure both sides of these equations are equal.

Houghton Mifflin Math Grade 5