For rectangular regions measured in whole-number units, the missing length or width is found by relating area to the product of the two dimensions: unknown side = area ÷ known side. An area model or array connects the quotient to equal rows or columns, while multiplication verifies the result and distinguishes area from perimeter; more advanced cases involving fractional or decimal dimensions, nonrectangular shapes, or generalized algebraic formulas are not included.
The area of a rectangle tells how many square units cover it. For a rectangle,
If one side is missing, divide the area by the known side:
Example: A rectangular garden has an area of square meters. Its length is meters. What is its width?
Write what you know:
Divide the area by the known length:
You can picture this as an array with columns and rows. It has squares altogether.
Check your answer with multiplication:
Since the product matches the area, the width is correct. Remember, area uses multiplication of the two side lengths; it is not the distance around the rectangle, which is the perimeter.
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