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How to Evaluate Expressions & Combine Like Terms

In math, "evaluate" means to simplify an expression, or mathematical phrase, to a single numerical value. Expressions often contain variables, which can make evaluation seem more complicated than it really is. To make it easier, first combine like terms. A term is a part of an expression; like terms are terms with the same variable. (The constants are like terms, too.) If you know the order of operations and can add, subtract, multiply and divide, you can combine like terms and evaluate any expression.

Things You'll Need

Calculator

Instructions

- 1
  Copy the expression from your textbook or worksheet onto a piece of paper so you can work with it.
- 2
  Determine the like terms -- the terms with the same variable as well as the constants -- in your expression. For example, if the expression is 4x + 2y + 6x + 9 +2y +8, the like terms are 4x and 6x, 2y and 2y, and the constants 9 and 8.
- 3
  Combine the like terms using addition or subtraction. For example, combining the like terms in the expression 4x + 2y + 6x + 9 +2y +8 -- 4x+6x, 2y+2y and 9+8 -- results in 10x + 4y +10.
- 4
  Plug numerical values in for the variables to evaluate the expression. For example, if your expression is 10x + 4y +10 with x = 5 and y = 1, it would look like this once you replace the variables with numbers: 10(5) + 4(1) + 10
- 5
  Simplify the expression to a single numerical value. Remember to follow the order of operations -- multiplication and division first, then addition and subtraction, and work from left to right. For example, the expression 10(5) + 4(1) +10 simplifies to 50 + 4 + 10, which is 64.

Numerology