The area of a square is equal to the area of a rectangle. The rectangle’s length is 5 cm more than the side of the square, and the rectangle’s breadth is 3 cm less than the side of the square. Find the perimeter of the rectangle in cm, assuming both shapes have exactly the same area.

Difficulty: Hard

Correct Answer: 34 cm

Explanation:


Introduction / Context:
This problem combines algebra with mensuration. You are told a square and a rectangle have equal area, but the rectangle’s sides depend on the square’s side. The correct method is to let the square side be s, write the rectangle dimensions as (s + 5) and (s - 3), equate areas, solve for s, then compute the rectangle perimeter 2 * (l + b).


Given Data / Assumptions:

  • Square side = s cm
  • Rectangle length = s + 5 cm
  • Rectangle breadth = s - 3 cm
  • Areas are equal: s^2 = (s + 5)(s - 3)
  • Perimeter of rectangle = 2 * (length + breadth)


Concept / Approach:
Form an equation using equal areas, solve for s, then substitute to find rectangle sides and perimeter. Ensure the breadth stays positive (s must be greater than 3).


Step-by-Step Solution:

Step 1: Set up area equality: s^2 = (s + 5)(s - 3) Step 2: Expand RHS: (s + 5)(s - 3) = s^2 + 2s - 15 Step 3: Equate: s^2 = s^2 + 2s - 15 Step 4: Cancel s^2: 0 = 2s - 15 => s = 7.5 Step 5: Rectangle length = 7.5 + 5 = 12.5 cm Step 6: Rectangle breadth = 7.5 - 3 = 4.5 cm Step 7: Perimeter = 2 * (12.5 + 4.5) = 2 * 17 = 34 cm


Verification / Alternative check:
Square area = 7.5^2 = 56.25. Rectangle area = 12.5 * 4.5 = 56.25. Areas match, so the perimeter computed from these rectangle sides is consistent.


Why Other Options Are Wrong:

26 cm or 18 cm: imply smaller side sums that would not preserve the equal-area relationship. 15 cm: too small for a rectangle whose length must exceed the square side by 5. 38 cm: would require larger sides than (12.5, 4.5) while still matching the square area.


Common Pitfalls:
Students often forget to expand correctly, or incorrectly cancel terms. Another mistake is using perimeter of square instead of rectangle. Also, do not assume s is an integer; s can be fractional as seen here.


Final Answer:
34 cm

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