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Puzzle Details

The surface area of a spherical balloon measured in square inches is the same as its volume, measured in cubic inches. What is the diameter of the balloon?

[Ref: ZEZW]

Answer: 6 inches. The surface area of a sphere, of radius r, is 4 * Pi * (r ^ 2) and the volume is (4/3) * Pi * (r^3). Putting these equal and cancelling gives r = 3, which means the diameter is 6 inches. QED.

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