<< Back to Lessons Index

7th Grade Math / Lesson 3: Evaluating Expressions and Identifying Equations


Evaluating Variable Expressions
What will we be learning in this unit?


  • This unit will review some basic terms and concepts needed to continue through this math class.
  • Today's lesson will cover evaluating variable expressions and equations.



Evaluating Variable Expressions


  • To evaluate a variable expression: substitute the value given for the variable(s) then follow the Order of Operations.

    Evaluate P = 2L + 2W when L = 2 and W = 3.

  • Substitute    P = 2(2) + 2(3)
  • Multiply          P = 4 + 6
  • Add               P = 10

    Practice

    Evaluate J = 4 + 6H - 2M when H = 3 and M = 4



Evaluating Variable Expressions


    Solution

    Evaluate J = 4 + 6H - 2M when H = 3 and M = 4

    Substitute    J = 4 + 6(3) - 2(4)
    Multiply        J = 4 + 18 - 8
    Add              J = 22 - 8
    Subtract      J = 14



Equations


  • Equation: must have an equal sign

    Which of the following are equations?

    A. 4 - 2 = n     B. X + Y = 3
    C. 6 * D          D. 4 + 7 = 11



Equations


  • Equation: must have an equal sign

    Which of the following are equations?

    A. 4 - 2 = n     B. X + Y = 3
    C. 6 * D          D. 4 + 7 = 11

    Solution :

    A is.          It has an equal sign.
    B is.          It has an equal sign.
    C is not.   It does not have an equal sign.
    D is.         It has an equal sign.