McKinsey, BCG, and Bain mostly dropped classic brain teasers as a hiring filter. If your invite is a case, PEI, and maybe an online test, spend your time there. This page exists because puzzles still appear at some economic consultancies, some boutiques, and the occasional office with a nostalgic interviewer. Do not build a 4-week teaser plan. Do not confuse a riddle with a case.
Case method: prep guide. Unstructured cases (no exhibits, you build a tree) are a different skill: unstructured.
Why MBB moved on
Brain teasers rewarded puzzle-camp kids and created noise. Cases are closer to the job. Official firm prep pages emphasize structured business problems, not “why are manhole covers round?” as the main event. If a partner still asks one, it is often a warm-up or a composure test, not the offer.
Where they still show up
- Economic consulting and some litigation-support firms (logic + estimation)
- A few engineering-heavy or quant interviews mixed into “consulting”
- Odd partner preferences (you cannot predict this from a blog)
If your target list is NERA, Compass Lexecon, Bates White, CRA, and similar, a logic/estimation warm-up is more plausible than at BCG London. Still confirm with recent candidates. CoachNed is not affiliated with those firms and does not run a 44-puzzle product as core prep.
If one appears: treat it like a mini unstructured case
- Restate the question. Confirm what “best” or “always” means.
- Say the approach. Estimation vs logic vs constraint satisfaction.
- Make assumptions explicit. Population, rates, geometry.
- Compute out loud, rounded.
- Sanity-check. Does the order of magnitude survive?
- Land. A number or a decision, plus the sensitive assumption.
That sequence is closer to market sizing and hypothesis than to trivia.
Three short examples (to show the method, not to memorize 44)
Estimation. “How many piano tuners in Chicago?” Population → households → piano ownership → tuning frequency → tuners’ capacity. Land in a range. The rec is the range plus the shakiest assumption (ownership rate).
Logic. “Three lights, three switches, you can visit the basement once.” Classic constraint puzzle: use heat vs light as extra state. Talk the states; do not go silent.
Fermi with a twist. “Should the city add a ferry?” This is often a tiny case hiding as a teaser. Draw a tree (demand, cost, substitution from other modes). If they wanted a riddle, they will stop you. If they wanted a case, you just started well.
What not to do
- Laugh and say “I hate these”
- Dump a memorized manhole-cover speech unprompted
- Spend October on riddle books instead of exhibits
- Confuse IQ-test culture with MBB 2026
Aptitude tests (Solve, Casey, CCA, SOVA, SHL) are the real “tests.” Those are not brain teasers either.
How much to practice
If you are MBB-only: zero dedicated teaser hours unless a recent office report says otherwise. If you are econ-consulting: a handful of Fermi estimates and one logic puzzle a week, max, while still casing. CoachNed’s 63 cases and 550+ drills will not include a manhole-cover module; that is intentional.
A Fermi you can reuse as method (not as an answer key)
“How many container ships call on Rotterdam each year?” You do not need the real statistic in the room. Structure: European import volumes or a port-rank guess → calls per week → weeks. Say the shakiest step (you do not know transshipment). Land in a range. If they wanted a case, they will now hand you an exhibit. If they wanted a puzzle, they will nod and move on.
Do not memorize 44 of these. Do memorize the habit: structure, assumptions, range, sanity check. That habit is already market sizing. Teaser books that hide the structure and print a cute answer teach the wrong sport.
Frequently asked questions
Should I prepare 44 worked teasers?
No. Method plus a few Fermi reps if your firms use them.
Is a market-size a brain teaser?
No. Market-size is a standard case module.
What if I freeze?
Label the pause, restate the question, pick estimation vs logic. Stress.
Next step
If your firms are MBB, sit a case. If your firms are econ consultancies, do one Fermi estimate tonight, then still sit a case.
CoachNed is independent and unaffiliated with McKinsey, BCG, Bain, or other firms. Cases on CoachNed are AI-simulated.