A probability sprint built from interview question types

Most first-round quant and trader interviews include quick probability questions: the chance two cards are both aces, the expected number of rolls to see a six, the probability a test result is a true positive. Knowing the method is not enough on the day. You have to set the question up in seconds and get the arithmetic right with someone watching.

The trainer generates these questions from templates, with new numbers each time, so you cannot memorise the answers. Easy covers counting with dice, coins and cards; Medium adds conditional probability, drawing without replacement and expected values; Hard adds Bayes, waiting times, gambler's ruin and recursive games. Answer as a fraction, a decimal or a percentage. A correct answer scores +1, a wrong one −1, and the clock keeps running.

After each answer the correct value and a one-line method stay on screen while the next question loads, so you learn without stopping the sprint. At the end you see correct answers per minute, accuracy by topic, the questions that took longest, and every question with its full working.

What probability questions come up in quant trading interviews?

Short counting and conditioning questions with dice, coins and cards, expected values of simple games, Bayes problems such as false positives, and waiting-time questions such as the expected flips to see two heads in a row. Speed and a clean setup matter as much as the method.

How is the probability trainer scored?

+1 for each correct answer and −1 for each wrong one, inside a fixed time. The results show your net score, accuracy, correct answers per minute and accuracy by topic.

Can I answer with fractions?

Yes. Type 7/36, 0.1944 or 19.44%. Decimals within 1% of the exact answer are marked correct; whole-number answers must be exact.

Is the probability trainer free?

There is a free sample run with no signup: a full 3-minute sprint at Easy with the working after each answer and a full review. Medium, Hard, mixed and adaptive levels, topic filters, other durations, learn mode and your history are part of QuantVault Pro.

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