Rectangle — Area 144 cm^2 and Sides in Ratio 4 : 9: Find the perimeter of the rectangle.

Difficulty: Easy

Correct Answer: 52 cm

Explanation:


Introduction / Context:
When area and side ratio are known, scale factor k follows from (4k)*(9k) = 144. After finding sides, compute the perimeter. This avoids solving two unknowns independently by leveraging the ratio constraint.



Given Data / Assumptions:

  • Sides = 4k and 9k (cm)
  • Area = 144 cm^2
  • Perimeter P = 2(4k + 9k)


Concept / Approach:
Compute k^2 from area and take the positive root. Then compute perimeter directly. Keep units in centimetres consistently.



Step-by-Step Solution:

(4k)(9k) = 36k^2 = 144 ⇒ k^2 = 4 ⇒ k = 2.Sides: 8 cm and 18 cm.Perimeter P = 2(8 + 18) = 52 cm.


Verification / Alternative check:

Area check: 8 * 18 = 144 cm^2 (matches).


Why Other Options Are Wrong:

  • 56, 60, 64 arise from incorrect k or arithmetic.
  • 48 assumes equal sides (square), which is not given.


Common Pitfalls:

  • Using 4 + 9 = 13 as area; remember area uses multiplication.


Final Answer:
52 cm.

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