Easy · Expected Value & Decision Theory · Numerical · ~4 min · #51

The Advantage of Flipping First

Real interview · Jane Street

You and an opponent take turns flipping a fair coin. The first person to flip heads wins 30 dollars from the other.

What is the expected profit of the player who flips first? (This is what going first is worth relative to a fair, zero-value game.)

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Worked solution

Give the problem an honest attempt first, then reveal the full explanation.

Reported in interviews

Jane StreetGlassdoor interview question

Candidate-reported and unverified; the firm may phrase it differently or no longer ask it. The wording here is our own paraphrase, and the solution was written and checked independently of any answers posted at the source.

Concepts

First-step analysisGeometric series

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