Find and interpret perimeter and circumference in numeric and contextual problems.
Write the right boundary expression from a description
Problem
A rectangle has length \(9~\text{units}\) and width \(4~\text{units}\). Write an expression for its perimeter.
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What this problem is really about
The requested expression should represent one complete trip around the rectangle without needing to evaluate it. Account for both copies of the length and both copies of the width, then substitute the given dimensions into that perimeter structure. Multiplying the dimensions would describe the interior area, while using each only once would cover just half the boundary.
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