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Candidates report a betting round with a deck of cards in SIG, Optiver and Five Rings interviews. The interviewer turns a card, you say whether the next one will be higher or lower, and you choose how much of your chips to put on it. The cards do not go back, so a deck that started even gets lopsided fast: with the 5 showing and the 2, 3 and 4 already gone from a 13-card suit, 8 of the 9 cards left beat the 5. The skill being tested is not the call, which is usually obvious, but the size of the bet.
This game deals that exercise and grades every stake. Before each card you pick a side and an amount out of a $1,000 bankroll. When the card turns you see the count, the chance your side wins, the Kelly stake, the press zone our score rewards, and where your stake sat on the growth curve. At the end you get a skill score out of 100, your bankroll against a Kelly bettor and a press-zone bettor on the same cards, and a bet-by-bet table.
Scoring: any stake from Kelly up to the top of the press zone (1.5 to 2 times Kelly, capped halfway between Kelly and all-in) earns full marks for that card. In 60,000 simulated 13-card decks, betting the middle of the zone averaged 136 times the starting bankroll against 100 times for Kelly, with a lower median (49 times against 54) and about a 1 in 2,000 chance of ending under 5% of the bankroll. Uncapped 2x Kelly lost 95% or more of the bankroll in 46% of decks.
Count the cards left that win and lose for your side. At even money the Kelly stake is (winners minus losers) divided by the cards that settle the bet. With 8 higher and 1 lower left, Kelly is 7/9, about 78% of your bankroll on higher.
Kelly gives the fastest long-run growth when betting never stops, so a Kelly stake always earns full marks here. A deck is only about 12 bets, and interviewers running these rounds tend to reward pressing an edge you have counted, so stakes up to the press zone (1.5 to 2 times Kelly, capped halfway to all-in) also score full marks. Pressing raises the average result and widens the spread.
In the 13-card deck ties cannot happen. In full-deck runs a card of the same rank pushes: your stake comes back, and Kelly uses only the cards that settle the bet.
There is a free sample run with no signup: one full 13-card deck of 12 bets, each reviewed against Kelly, ending in a skill score. Full-deck runs, prop bets at posted odds, the bet clock and your history are part of QuantVault Pro.
Related: Kelly criterion guide · Fermi estimation questions · Probability interview questions · SIG betting and market-making round · All trading games