Equal areas: circle vs square — compare diameter and diagonal:\nIf a circle and a square have equal areas, what is (diameter of circle / diagonal of square)^2?

Difficulty: Medium

Correct Answer: 7/11

Explanation:


Introduction / Context:
Equate the areas to relate the circle radius to the square side. Then express the requested squared ratio in those terms. Using π = 22/7 gives a clean rational result matching options.


Given Data / Assumptions:

  • Area(circle) = Area(square).
  • Let circle radius = r, square side = s.
  • Use π = 22/7 for final numeric comparison to options.


Concept / Approach:
πr^2 = s^2 ⇒ (diameter/diagonal)^2 = (2r / (s√2))^2 = (4r^2)/(2s^2) = 2r^2/s^2 = 2/π.


Step-by-Step Solution:

From equality: s^2 = πr^2.(diameter/diagonal)^2 = 2r^2 / s^2 = 2 / π.With π = 22/7, 2/π = 2 / (22/7) = 14/22 = 7/11.


Verification / Alternative check:
Direct substitution with any r (e.g., r = 1) produces the same 2/π expression; rationalizing with 22/7 yields 7/11.


Why Other Options Are Wrong:
11/7 and 9/7 invert the correct value; 7/9 mismatches; 2/π is the unsimplified exact form but the keyed answer is its 22/7 evaluation.


Common Pitfalls:
Comparing diameter to side (not diagonal), or forgetting the √2 for the square’s diagonal.


Final Answer:
7/11

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