Paid a dollar or the draw

You draw XX from a continuous Uniform distribution on [0,1][0,1]. If X>12X > \tfrac12 you are paid a flat $1; otherwise you are paid XX dollars. What is the expected payout (in dollars, to four decimals)?

Show hints (2)+
  1. Split at 1/2: a flat-$1 branch weighted by P(X>1/2)P(X>1/2), plus 01/2xdx\int_0^{1/2} x\,dx for the paid-X branch.
  2. The integral 01/2xdx=1/8\int_0^{1/2} x\,dx = 1/8 already carries the density; add it to 12×1\tfrac12\times 1.

Answer

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0.625 (± 0.001)

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Asked at: Multi-Strategy Quant, Mixed Quant & Coding

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