The yard behind the Cindy’s house is rectangular in shape and has a perimeter of 72 feet. If the length l of the yard is 18 feet longer than the width w of the yard, what is the area of the yard, in square feet?

Answer :

Think of it like this.  The perimeter is 72 feet.  The length, l, is 18 feet longer than the width, w.  So, l=w+18.

Perimeter is calculated by adding the lengths of all four sides together, AKA adding the length twice and the width twice: l+w+l+w.

Since l=w+18, we can substitute this in for l in the expression above: l+w+l+w=w+18+w+w+18+w

Simplified, we combine like terms, the w's and the 18's: 4w+36.  This is the perimeter.

The perimeter is 72 feet, so 72=4w+36.  To find the width, we need to isolate w.  First, subtract 36 from both sides: 72-36=4w+36-36.  Simplified: 36=4w.  Then, divide 4 on both sides to get w alone.  36/4=4w/4.  w=9.  Therefore, the width of the rectangle is 9 feet.

Since the length of the rectangle is w+18, and w=9, we know that l=9+18=27.  So w=9, and l=27.  The length is 27 feet.

In a rectangle, we find area by multiplying length by width: A=lw.  To find the area of the yard, multiply 27 by 9: A=27*9=243.  Since 27 and 9 are both measurements in feet, the answer is 243 square feet.

Answer: The area of the yard is 243 square feet.

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