Four points on a semicircle

MediumProbability~6m

Four points are dropped independently and uniformly at random on the circumference of a circle. What is the probability that all four lie within some common semicircle? (to 3 decimals)

Show hints (2)+
  1. Anchor the semicircle to a "leader" point that has all the others clockwise within 180∘180^\circ - and argue the leader is unique.
  2. A fixed point is the leader with probability (1/2)3(1/2)^3; sum over the four disjoint leaders.

Answer

Reveal answer →

0.5 (± 0.001)

Create a free account to see the full worked solution and track your progress.

Interview format: Market Maker, Hedge Fund Quant

Related questions