AlgebraVery hardRectangle length from two perimeters
Algebra practice question
A rectangle has a perimeter of 36. If its length were doubled and its width halved, the perimeter would be 42. What is the length of the original rectangle?
Answer: 8
2L + 2W = 36 gives L + W = 18. The changed rectangle gives 2(2L) + 2(W/2) = 42, or 4L + W = 42. Subtracting: 3L = 24, so L = 8.
Common wrong answers
- If you answered 6
- 6 comes from 3L = 18.
- If you answered 10
- 10 is the width.
- If you answered 18
- 18 is L + W.
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