How to Use a Formula to Evaluate a Variable
A formula is an equation that is used often. Common formulas exist for finding area, circumference, perimeter, distance, percent and volume, among other quantities. Formulas use variables to stand for the components of the equation. Variables are letters or symbols that represent numbers. You can use a formula to find the value of variables using the "formula-substitute-solve" technique.
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Instructions
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Choose the proper formula. For example, if you are asked to find the percent of a given quantity, you will need to use the percent formula, or part of base equals percent times base. If you need to find the height of a cylinder, you would use the volume formula of volume equals area times radius squared times height. Your math book and class notes should include all relevant formulas for your particular mathematics studies.
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Substitute known values for variables. For example, imagine we are using the formula for perimeter of a rectangle: P = 2l + 2w, or perimeter equals two times length plus two times width. For this problem, we are given the measurements for length (10 cm) and width (8 cm). To complete the "substitute" portion of the problem, we would rewrite the formula as: P = (2 x 10) + (2 x 8)
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Use the rules of algebra and the order of operations to solve the problem. Going back to our perimeter problem, this means that we need to complete the multiplication next. According to the order of operations, multiplication should be completed before addition. Since 2 x 10 is 20 and 2 x 8 is 16, we would rewrite the problem as:P = 20 + 16 Finally, we add to solve for perimeter. 20 + 16 is 36, so our answer is perimeter equals 26 cm.
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Tips & Warnings
Never forget to include units in your final answer. For example, if you are finding the area of a parallelogram with a base of 3 inches and height of 7 inches, the area will be 21 square inches.
