AlgebraMediumRectangle with the same perimeter as a square
Algebra practice question
A rectangle's width is 5 centimetres less than its length. Its perimeter equals the perimeter of a square with side length 10 centimetres. What is the length of the rectangle, in centimetres?
Answer: 12.5 or 25/2
The square's perimeter is 40. For the rectangle: 2(l + l − 5) = 40 → 4l − 10 = 40 → l = 12.5.
Common wrong answers
- If you answered 10
- 10 is the square's side, not the rectangle's length.
- If you answered 15
- 15 comes from 2l − 5 = 25 solved as l = 15, halving only once.
- If you answered 7.5
- 7.5 is the width.
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