How to solve for the length of a rectangle given its perimeter

Question
If the length of a rectangular parking lot is 10 meters less than twice the width, and the perimeter is 100 meters, find the length of the parking lot




Solution
First, write the word problem as an equation.
Let x = width of the rectangle
Then 2x - 10 = length of the rectangle
Then its perimeter is 2x + 2(2x - 10) = 100

The perimeter of a rectangle is computed as 2L + 2W

Simplify the above formula 2x + 4x - 20 = 100 ===> 6x = 120
Therefore x = 20

The length of the rectangle is 30 AND its width is 20.

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