GTS Probability & Mental Math Interview

What the round is, what GTS asks, and how to prepare, from candidate reports and the QuantVault practice set.

Stage 3 of 545-60 min20 practice problemsUpdated October 20, 2026

The GTS Probability & Mental Math interview is stage 3 of 5 in the GTS interview process, after the Online Assessment / Coding. Format: 45-60 min - video. Probability, expectation, combinatorics, and brain-teasers -- card-guessing EV (harmonic numbers), races, counting.

Preparing for this round? Practice the 20 questions mapped to the GTS Probability & Mental Math, with worked solutions. A free account saves your progress.

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What the Probability & Mental Math tests

QuantVault maps 20 practice problems to this round. By topic, the biggest groups are probability (8), expectation (6), brain teasers (4), combinatorics (2); by difficulty, 6 easy, 14 medium and 0 hard. 2 of them were reported by candidates who interviewed at GTS, most recently in Jul 2026.

How to prepare for the Probability & Mental Math

Linearity of expectation -- card-guessing (H_52).
Counting + combinatorics cleanly.
Estimate, then formalize.

Further reading: Mental math for trading interviews · How quant superdays work · Behavioral questions at trading firms · Market-making game interview guide.

Question types in this round

The 4 largest question types in the GTS Probability & Mental Math practice set; across them the most common sub-topics are expected value, discrete probability, independence, conditional probability, symmetry, game theory. The questions themselves, with worked solutions, are in the round practice.

Prepare with QuantVault

PracticePractice the Probability & Mental Math round20 mapped problems, 5 free Interview funnelAll 5 GTS roundsThe full funnel, a practice set for each stage Firm guideGTS interview guideEvery round, tracks, timeline, pay and a prep plan Online assessmentGTS online assessment guideFormat and practice Problem setGTS interview questionsEvery question tagged to this firm Related problemsProbability interview questionsWorked solutions CourseProbability course7 lessons GameZetamac mental-math gameTimed arithmetic drill Game80 in 8 mental-math test80 questions, 8 minutes Next roundStatistics45-60 min - video

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Frequently asked questions

What is the GTS Probability & Mental Math interview?

It is stage 3 of 5 in the GTS interview process, after the Online Assessment / Coding. Format: 45-60 min - video. Probability, expectation, combinatorics, and brain-teasers -- card-guessing EV (harmonic numbers), races, counting.

How long is the GTS Probability & Mental Math interview?

Candidates report: 45-60 min - video.

What questions come up in the GTS Probability & Mental Math interview?

The practice set QuantVault maps to this round centers on probability, expectation, brain teasers.

How should I prepare for the GTS Probability & Mental Math interview?

Linearity of expectation -- card-guessing (H_52). Counting + combinatorics cleanly.

What comes after the Probability & Mental Math?

The Statistics (stage 4 of 5). Format: 45-60 min - video.

Practice the GTS Probability & Mental Math round

Work the 20 mapped practice problems with progress tracking, then move to the next stage of the GTS funnel.

Practice the Probability & Mental Math round Create a free account GTS interview guide GTS online assessment All 5 rounds