Brain Teasers

Challenge your logical thinking with classic interview puzzles.

Looking for math practice? See the complete case interview math guide →

Session Length

Difficulty

Tips

💡Take your time - these puzzles require careful thinking
💡Hints are available but reduce XP earned
💡Explanations provided after each puzzle

What these brain teasers are for

Brain teasers test the part of an interview that has no formula: what you do when the path to the answer is not obvious. The 150 puzzles here are consulting-focused rather than generic riddles — most are either business quantitative problems posed as puzzles, or logic and probability questions of the kind that get folded into a case.

Every puzzle carries a hint you can reveal when stuck, and a full explanation afterwards that shows the reasoning rather than just the answer.

The three difficulty levels

Foundation (35 puzzles): Warm-up logic and single-step business puzzles. Worst-case reasoning, simple probability, straightforward margin and revenue questions. If you are new to brain teasers, everything you need to learn the format is here.
Standard (60 puzzles): The band that matches a real first-round interview. Multi-step probability, expected value, optimisation under a constraint, and estimation questions with no clean answer. This is where most preparation time belongs.
Advanced (55 puzzles): Game theory, information theory, combinatorics and the harder classics. Considerably above what most interviews ask, which is the point — they make the standard set feel routine.

What the puzzles cover

Puzzles are tagged by the reasoning they demand. The distribution reflects what consulting interviews actually ask:

Logic (71 puzzles): The largest category. Deduction, worst-case reasoning and problems where the trick is noticing what the wording actually permits.
Probability (41): Conditional probability, independence and the classic traps where intuition and arithmetic disagree.
Optimisation (38): Finding the best outcome under a constraint. Common in operations and supply chain cases.
Estimation (32): Fermi-style questions with no exact answer, judged entirely on whether your chain of assumptions holds up.
Game theory (18): Two-party problems where you have to reason about what the other side will do. A favourite in later rounds.
Expected value (16): Weighing outcomes by probability. Underpins most pricing, bidding and risk questions.
Business quantitative (~40 across tags): Market sizing, pricing, profitability, breakeven, growth, ROI, capacity and customer economics posed as puzzles rather than as cases.

How to approach a brain teaser in an interview

Restate the problem before solving it

Say back what you have been asked, including any constraint you think applies. Half of all brain teaser failures are answering a subtly different question, and restating catches that in ten seconds.

Say your assumptions out loud, and label them as assumptions

On an estimation question the interviewer cannot check your answer either. What they can check is whether each assumption is defensible and whether you flagged it as a choice rather than smuggling it in as a fact.

Look for the worst case, not the average case

Any puzzle containing the word "guarantee" is asking for the worst case. Drawing from a jar to guarantee ten of one colour means assuming the draws go against you for as long as they possibly can.

Sanity-check the direction before the magnitude

Ask whether the answer should be bigger or smaller than the number you started with, and roughly by how much. Getting the direction wrong is a reasoning error; getting the magnitude slightly wrong is usually just arithmetic.

Never go quiet

Silence is the only unrecoverable move. If you are stuck, narrate the approaches you are considering and why you are discarding them. That is the behaviour the question was designed to observe.

Where these fit alongside the other trainers

Brain teasers train judgement under uncertainty. Mental math sprints train raw speed, and case math drills train picking the right calculation from a business scenario. Most candidates need all three, weighted towards case math. A study plan sequences them for you.

Frequently asked questions

How many brain teasers are there?

150 in total: 35 at Foundation, 60 at Standard and 55 at Advanced. They are drawn at random each session, so repeating a difficulty gives you a different set.

How long is a session?

A Quick Session is 2 puzzles and takes roughly 3 to 5 minutes. A Deep Session is 4 puzzles and takes 8 to 12. There is no clock on individual puzzles, because brain teasers test reasoning rather than speed.

Do consulting firms still ask brain teasers?

Less than they did a decade ago, and McKinsey, BCG and Bain rarely ask the pure riddle type any more. What replaced them is estimation and structured-logic questions inside a case, which is the same skill in a different wrapper. Boutique firms, and finance interviews generally, still ask them directly.

Should I use the hints?

Yes, once you are genuinely stuck rather than merely uncomfortable. Sitting with a puzzle for two or three minutes is where the learning happens; sitting with it for fifteen is not. Every puzzle also carries a full explanation afterwards, which is worth reading even when you answered correctly.

What is the interviewer actually assessing?

How you think when you do not immediately know the answer. Stating your assumptions, choosing a structure, and narrating the reasoning matters more than arriving at the number. A candidate who reasons out loud to a wrong answer usually scores better than one who goes silent and gets it right.

Is it free?

Yes, and no signup is required. A free account only adds saved history across devices.