Consulting Brainteasers: The Evidence, a Method and 7 Puzzles

Do consulting firms still ask brainteasers?

Rarely, at the top firms. McKinsey's official guidance describes every interview as a personal experience component paired with a case, and it describes no separate puzzle round (official). Two large prep providers, writing in 2026, agree that McKinsey, BCG and Bain almost never ask brainteasers and that tier-2 firms ask them occasionally. They disagree on the Big Four (reported).

Hacking the Case Interview adds that candidates it coached met brainteasers in roughly 30-40% of interviews at firms such as Accenture, Capgemini and smaller boutiques. Both tables rest on coaching experience and no firm publishes data, so read them as estimates. If you apply only to MBB, a brainteaser is unlikely. If you apply more widely, prepare a few.

What the research says about brainteasers in hiring

The evidence explains why large firms dropped them. In 2013 Google's head of people operations, Laszlo Bock, told the New York Times that brainteasers did not predict job performance and that structured behavioral interviews worked better (reported, ABC News).

A 2019 study by Highhouse, Nye and Zhang in Applied Psychology surveyed 736 working adults. Those who rated brainteasers as appropriate interview questions scored higher on narcissism and sadism and lower on social competence, and the team ran a replication with 496 people who make hiring decisions (reported, PsyPost).

The skill itself has a well-known measure. Shane Frederick's Cognitive Reflection Test (Journal of Economic Perspectives, 2005) uses three short puzzles to measure whether people override an intuitive wrong answer (official, academic summary). That habit is exactly what consulting firms still test, through structured formats.

Four types of brainteaser

A four-step method for any puzzle

1. Restate. Repeat the puzzle in your own words, list the constraints and confirm anything ambiguous.
2. Name the trap. Say your first instinct out loud, label it as a first guess, and ask yourself which detail it ignores.
3. Test. Write the equation, try a small or extreme case, or list every possibility.
4. Check. Test the answer against every constraint and state it in one sentence.

Seven practice puzzles with worked answers

All seven were written for this page. Puzzles 1-5 are new scenarios built on well-known puzzle types; puzzles 6 and 7 are original.

Puzzle 1: the lock and the bell (arithmetic trap)

A bike shop sells a lock and a bell for €33 together. The lock costs €30 more than the bell. Find the price of the bell. This is a variant of the bat-and-ball item in Frederick's test.

• Fast answer: €3.
• Worked answer: bell = b and lock = b + 30, so 2b + 30 = 33 and b = €1.50. Check: 1.50 + 31.50 = 33.
• Say out loud: "My instinct says €3, but then the lock costs €33 and the total is €36, so I'll set up the equation."

Puzzle 2: the courier's round trip (arithmetic trap)

A courier van drives 20 km to a customer at 60 km/h and returns on the same road at 30 km/h. Find its average speed for the round trip. This is a variant of the classic average-speed puzzle.

• Fast answer: 45 km/h.
• Worked answer: out takes 20 minutes, back takes 40, so 40 km in 60 minutes is 40 km/h. The van spends twice as long at the slower speed.
• Say out loud: "I'll work with time, because averaging speeds ignores how long each leg takes."

Puzzle 3: up 25%, down 20% (arithmetic trap)

A retailer raises a jacket's price by 25%, then offers 20% off the new price. Find the net change.

• Fast answer: +5%.
• Worked answer: 100 x 1.25 = 125, and 125 x 0.8 = 100. The net change is zero, because each percentage applies to a different base. The same logic drives most percentage traps in case math.

Puzzle 4: who built the model (logic)

Exactly one of three analysts built a financial model. Anouk says Bram built it. Bram says he did not. Chloe says she did not. Exactly one statement is true. Identify the builder. This is a variant of the truth-teller and liar type.

• Fast answer: Bram, because Anouk named him.
• Worked answer: test each case. If Anouk built it, Bram's and Chloe's statements are both true: two true, so no. If Bram built it, Anouk's and Chloe's are true: no. If Chloe built it, only Bram's statement is true. The builder is Chloe.

Puzzle 5: lanyards in the dark (logic)

A box in a dark room holds 12 red, 8 blue and 5 green lanyards. Find the minimum number you must take to be certain of (a) two of the same color and (b) two blue ones. This is a variant of the drawer, or pigeonhole, type.

• Fast answer: (a) 3 and (b) somewhere near 9.
• Worked answer: (a) the worst case is one of each color, so the fourth must match: 4. (b) The worst case is all 12 red and all 5 green first, then 2 blue: 12 + 5 + 2 = 19.
• Say out loud: "Certain means I plan for the worst possible draw."

Puzzle 6: elevator trips in an office tower (estimation)

Estimate how many elevator trips a 20-floor office building makes on a weekday.

• Fast answer: a number with no structure behind it.
• Worked answer: 19 office floors x about 80 people = about 1,500 people. Each rides 6 times: arriving, leaving, lunch down and up, and one meeting on another floor and back. That gives 1,500 x 6 = 9,000 rides. At an average of 3 riders per trip (full at peaks, nearly empty midday), the building runs about 3,000 trips. Sanity check: 6 elevators over 10 busy hours make 3,000 / 60 = 50 trips per elevator per hour, one every 72 seconds, which is plausible. The market sizing guide uses the same method.

Puzzle 7: the bakery that likes rain (lateral)

One store in a Dutch bakery chain sells more bread on rainy days than on sunny ones. Every other store shows the opposite. Give three explanations and a test for each.

• Fast answer: one story, such as "people buy comfort food when it rains".
• Worked answer: group explanations so they do not overlap. Location: the store sits in a train station, where rain moves cyclists onto trains; test with footfall by weather. Customers: local residents leave town for the coast on sunny days; test with loyalty-card data by postcode. Channel: the store fulfils the chain's home deliveries, which rise when people stay in; test by splitting sales by channel.

Where the same skill shows up today: Solve, logic tests and case math

McKinsey describes Solve as a gamified assessment of problem solving that candidates take alone, without outside tools or AI (official); our McKinsey test guide covers its format. Candidate reports describe verbal and logic sections in Kearney's test and critical reasoning and data sufficiency questions in L.E.K.'s (reported). Our assessment test comparison sets them side by side.

Inside the case itself, the trap from puzzle 3 returns whenever a percentage changes its base. Practicing puzzles builds the habit of checking a first answer before you say it.

What to say when you are stuck

1. State what you know and where you are blocked.
2. Simplify: smaller numbers, an extreme case or a drawing.
3. Ask one clarifying question.
4. If time runs out, give your best answer, your reasoning and how you would verify it.

McKinsey's case guidance says there is no single correct solution, and interviewers judge an odd question the same way: by the reasoning. Freezing or guessing silently is one of the case interview mistakes that costs most. Cracking the Case sets out a brainteaser approach with seven further practice puzzles, alongside its guesstimate principles and three fully worked cases.