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Two random breaks giving triangle sides

Question

A one-metre stick is broken at two points chosen independently and uniformly along its length, producing three pieces. What is the probability that these three pieces can be the sides of a triangle?

Short answer

14\tfrac14. The pieces form a triangle exactly when every piece is shorter than half the stick. With breaks x<yx<y this means x<12x<\tfrac12, y>12y>\tfrac12 and y−x<12y-x<\tfrac12, a triangle of area 18\tfrac18 inside the region x<yx<y of area 12\tfrac12.

Adapted from QuantQuestions.io; question and answer rewritten by SelfMadeQuant.com.

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