Landing in the ring

A point is chosen uniformly at random inside a disk of radius 11. What is the probability it lands in the ring between distance 12\tfrac12 and distance 34\tfrac34 from the center? (to 4 decimals)

Show hints (2)+
  1. Uniform over area, so compare areas; the ring is one disk minus another.
  2. Square both radii and subtract: (3/4)² − (1/2)².

Answer

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0.3125

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Asked at: Timed Mental-Math & Sequences, Game-Based Aptitude

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