Setting up percent word problems

When teaching students to solve word problems involving percentages, I start by teaching a generic formula that works for tax, tips, simple interest, discount, and finding the percentage.  I always teach students how to solve simple algebraic equations prior to this step, so they have the foundational skills of balancing an equation and solving for a variable.  The percentage formula is:

T x % = n

Total of percent is small number

Teaching both the formula and the words is important because word problems are in linguistic form and must be translated to a numeric equation.

Once the numbers given in a word problem are inserted in the formula, the student simply solves for the variable.  I have found students make less calculation errors by using this formula, than trying to remember whether to multiply or divide and selecting the wrong process.  I also encourage students to check to see if their answers are logical.  If the percentage is less that 100% or 1.00, then the "n" number should be smaller than the "T" Total.  If the percentage is exactly 100% or 1.00, then the 2 numbers should be the same.  If the percentage is over 100%, then the "n" number will be greater than the "T" Total.  Most word problems for upper elementary student will use percentages less than 100%.

When students are proficient at setting up the original equation and solving for the variable, then teach the second-step variations.  For tax and tips, add to the original Total.  For simple interest, multiply by number of years or a fraction of a year, then add to the original Total.  For discount, subtract from the original Total.


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