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:
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 cmVerification / 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
Discussion & Comments