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The perimeter of a rectangular picture frame is 30 inches. The length of the frame is three less than twice the width.
What are the dimensions of the frame?
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Let L be the length, W be the width.
Then the condition says:
L = 2W - 3.
The perimeter is L + W + L + W.
Substitute (2W-3) instead of L in the perimeter.
You will get for the perimeter this expression: (2W-3) + W + (2W-3) + W.
Or, combining the like terms, 6W - 6.
It is equal to 30, according to the condition:
6W - 6 = 30.
Then 6W = 30 + 6,
6W = 36,
W = 6 inches.
So, you just found the width. It is 6 inches.
Now, the length is 2W -3 = 2*6-3 = 9 inches.