Product of two uniforms above a half

Let X,Y∼Uniform(0,1)X, Y \sim \text{Uniform}(0,1) be independent. Compute P ⁣[XY>12]\mathbb{P}\!\left[XY > \tfrac12\right], rounded to the nearest hundredth.

Show hints (2)+
  1. For a fixed xx, the condition xy>12xy>\tfrac12 means y>12xy>\tfrac{1}{2x} - feasible only when x>12x>\tfrac12.
  2. Integrate the admissible yy-length 1−12x1-\tfrac{1}{2x} over x∈(12,1)x\in(\tfrac12,1); you'll meet a ln⁡\ln term.

Answer

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0.15 (± 0.01)

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