Hard Probability Interview Questions
These are the probability questions that separate candidates who know the technique from those who can apply it under pressure.
77 questions, all free to practise.
- A 12 before two 7sHardProbabilityStochastic ProcessesView →
- A coin thick enough to land on its sideHardProbabilityBrainteasersView →
- A half-plane, given positiveHardProbabilityRandom VariablesView →
- A rectangle over the shaded rowHardProbabilityCombinatoricsView →
- A second red ball from the same urnHardProbabilityConditional Probability & ExpectationView →
- A small sub-triangleHardProbabilityRandom VariablesView →
- A three-way race to the first headHardProbabilityRandom VariablesView →
- A void suit in bridgeHardProbabilityCombinatoricsView →
- Amoeba extinctionHardProbabilityStochastic ProcessesView →
- Bertrand's chordHardProbabilityBrainteasersView →
- Best-of-seven underdogHardProbabilityRandom VariablesView →
- Bluffing frequency in pokerHardProbabilityExpected ValueView →
- Branching process extinction (critical)HardProbabilityStochastic ProcessesView →
- Branching process extinction (supercritical)HardProbabilityStochastic ProcessesView →
- Broken-stick triangleHardProbabilityView →
- Buffon's needleHardProbabilityCalculusView →
- Cars advancing to the endHardProbabilityExpected ValueView →
- Connecting noodlesHardProbabilityExpected ValueView →
- Correlation of min and maxHardProbabilityRandom VariablesView →
- Counting fives before a four and a sixHardProbabilityRandom VariablesView →
- Counting two-pair handsHardProbabilityCombinatoricsView →
- Cuts until one orb remainsHardProbabilityExpected ValueView →
- Deriving the first-price shading factorHardProbabilityExpected ValueView →
- Distinct toys from seven boxesHardProbabilityExpected ValueView →
- Draws to pass a log thresholdHardProbabilityRandom VariablesView →
- Draws to pass twoHardProbabilityRandom VariablesView →
- Ehrenfest urn stationary distributionHardProbabilityStochastic ProcessesView →
- Everyone gets one of eachHardProbabilityCombinatoricsView →
- Exactly one pairHardProbabilityCombinatoricsView →
- Expected arc covering a fixed pointHardProbabilityExpected ValueView →
- Expected chord between two random pointsHardProbabilityExpected ValueView →
- Expected chord intersectionsHardProbabilityCombinatoricsView →
- Expected local maxima in a shuffleHardProbabilityExpected ValueView →
- Filling three bins from a coin flipHardProbabilityCombinatoricsView →
- Guessing cards from a known pileHardProbabilityExpected ValueView →
- HTH before HHTHardProbabilityRandom VariablesView →
- Head density with no two in a rowHardProbabilityCombinatoricsView →
- Hitting zero on a ringHardProbabilityStochastic ProcessesView →
- Laplace's rule of successionHardProbabilityConditional Probability & ExpectationView →
- Loops from tying noodlesHardProbabilityExpected ValueView →
- More coins, more heads?HardProbabilityCombinatoricsView →
- No two samples too closeHardProbabilityCombinatoricsView →
- Odd sums on a 3×3 gridHardProbabilityCombinatoricsView →
- One of each face before the two of heartsHardProbabilityCombinatoricsView →
- Only seven left unchosenHardProbabilityCombinatoricsView →
- Overshoot past oneHardProbabilityRandom VariablesView →
- Pairing gloves within oneHardProbabilityCombinatoricsView →
- Penalty kicks with a shifting rateHardProbabilityRandom VariablesView →
- Prisoners and the boxesHardProbabilityBrainteasersView →
- Range beats the midpointHardProbabilityRandom VariablesView →
- Reflected paths ending below the levelHardProbabilityStochastic ProcessesView →
- Rolling until two rolls are closeHardProbabilityExpected ValueView →
- Rounds to see all faces with two diceHardProbabilityExpected ValueView →
- Seven seated in age orderHardProbabilityCombinatoricsView →
- Shortest of three piecesHardProbabilityRandom VariablesView →
- Six pieces, none past a halfHardProbabilityRandom VariablesView →
- Smallest card sharing a boxHardProbabilityExpected ValueView →
- The all-pay auctionHardProbabilityExpected ValueView →
- The boy born on a TuesdayHardProbabilityConditional Probability & ExpectationView →
- The drunk passengerHardProbabilityConditional Probability & ExpectationView →
- The frog's single leftward hopHardProbabilityCombinatoricsView →
- The leap-frog's favorite landing spotHardProbabilityStochastic ProcessesView →
- The reroll advantage in a die duelHardProbabilityMarket Making & Betting GamesView →
- The two-envelopes paradoxHardProbabilityConditional Probability & ExpectationView →
- Three first-heads in non-decreasing orderHardProbabilityRandom VariablesView →
- Triangle from three independent sticksHardProbabilityCalculusView →
- Triangle that swallows the centerHardProbabilityBrainteasersView →
- Two Brownian values, both positiveHardProbabilityStochastic ProcessesView →
- Two coprime integersHardProbabilityCombinatoricsView →
- Two elements in the long cycleHardProbabilityCombinatoricsView →
- Two random segments overlappingHardProbabilityRandom VariablesView →
- Two random subsets that overlapHardProbabilityCombinatoricsView →
- Two walks returning togetherHardProbabilityCombinatoricsView →
- When a power of the process is a submartingaleHardProbabilityStochastic ProcessesView →
- When a uniform ratio rounds to a squareHardProbabilityRandom VariablesView →
- When the extremes sum above oneHardProbabilityRandom VariablesView →
- Will the three-legged table stand?HardProbabilityView →
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