Solving for Missing Dimensions (Area and Perimeter)

Solving for Missing Dimensions (Area and Perimeter)

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When you take the GED Math test, you will be given a sheet with all of the formulas for area and perimeter. Unfortunately, most of the questions on these subjects will require a bit more than plugging the given numbers into the formula and solving. You may be given the area or perimeter and then asked to solve for one of the other dimensions.


Solving for a missing dimension requires you to treat the formula like an algebraic equation: substitute the given numbers, and then rearrange the formula to isolate the unknown dimension.


Let's take a look at an example: A rectangle has an area of 24 square feet and a length of 3 feet. What is the width? We'll start with the formula for the area of a rectangle: A = 𝑙𝑤. Then, we plug in the given values: 24 ft² = 3 ft × 𝑤. To isolate the width on one side of the equation, divide each side by the length: 24 ft² ÷ 3 ft = 3 ft ÷ 3 ft × 𝑤. This leaves us with 8 ft = 𝑤, meaning that the width of the triangle is 8 ft. (Notice that the units are "unsquared" when the area is divided by the length.)


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