A half-plane, given positive

Let X,YX, Y be independent standard normal variables. Compute P[ Y>3 X ∣ Y>0 ]\mathbb{P}\big[\,Y > \sqrt{3}\,X \ \big|\ Y > 0\,\big].

Show hints (2)+
  1. The joint density is rotationally symmetric, so the direction angle is uniform - probabilities are angle fractions.
  2. Y>0Y>0 is 180°180°; Y>3XY>\sqrt3 X is Θ∈(60°,240°)\Theta\in(60°,240°). Intersect and divide.

Answer

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0.6667 (± 0.001)

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