Short answer
To beat a written case test such as the old McKinsey PST, read each question before the exhibit, extract only the numbers you need, calculate by hand with rounded figures, and pick the answer that serves the client's underlying objective. The PST is retired, but this method still works for Solve, written cases at other firms and data-heavy interviews.
Key takeaways
- Read the question first, then scan the passage and exhibits for the specific data it needs.
- Round aggressively and check orders of magnitude; most wrong math answers are off by a factor of 10.
- The best answer serves what the client is ultimately trying to achieve, which may differ from what they literally asked.
- The McKinsey PST is retired; McKinsey now uses Solve, which rewards the same reading and reasoning habits.
The short version: three skills decide your score
A written case test measures three things: how precisely you read, how cleanly you calculate without a calculator, and whether you understand what the client is trying to achieve. The McKinsey Problem Solving Test (PST) tested all three in 60 minutes. It is retired now, and McKinsey screens with Solve, a gamified assessment. The three skills carry over directly.
I took the PST on paper, passed, and went on through the case rounds. Later I wrote practice tests and coached candidates on the same format. What follows is the method I used and taught.
How the test was built
The PST gave you a booklet of business cases with about 26 multiple-choice questions and 60 minutes to answer them. Each case opened with a short introduction to a fictional client, followed by text, tables and charts. A question from the client framed the problem. Later questions in a case often introduced new data, so the case grew more complex as you went.
The time pressure was real: just over two minutes per question, including reading. Candidates who read every word of every exhibit ran out of time on the last case.
Skill 1: read the question before the case
The single biggest time saver is reading the question before the detail. Skim the introduction for context (who the client is, what they sell, what worries them). Then go to the question and only then into the text and exhibits.
- Read the case introduction in 20-30 seconds.
- Read the question and all answer options.
- Identify what the question needs: a number, a direction, a cause.
- Scan the exhibits for exactly that data and ignore the rest.
- Answer, mark your confidence, move on.
Answer options are information too. If all four options are between 8% and 12%, you need precision. If they range from 2% to 200%, an order-of-magnitude estimate is enough.
Skill 2: do clean math without a calculator
The PST banned calculators, and Solve offers only a basic in-game calculator in some games. Either way, speed comes from mental shortcuts.
- Round early. 4,870 x 0.31 is roughly 4,900 x 0.3 = 1,470. Check whether the options are far enough apart for that to work.
- Track zeros. Write large numbers in thousands or millions. Most wrong answers I saw while coaching were off by a factor of 10.
- Use fractions. 12.5% is 1/8, 33% is 1/3, 20% is 1/5.
- Sanity check. If a small bakery's profit comes out at $40 million, something went wrong.
My case interview math guide lists the shortcuts that come up most.
Skill 3: find the client's real objective
This is where most smart candidates lose points, and I learned it on my own test.
One of the cases in my PST was about a fish restaurant. The owner planned to serve slightly less fresh fish on each plate. The question asked what the owner was trying to achieve. The options included lowering prices, cutting costs, raising profit and raising sales. Each sounded reasonable. Reading carefully, the owner wanted to use the savings to lower prices so that more people would come in. The best answer was the one about attracting more customers. Cost cutting was only the mechanism toward that goal.
A later question in the same case asked whether the chef should buy an automatic shrimp peeler. That one was a straightforward investment calculation, and it felt easy after the trap in the first question. The lesson stayed with me: always ask what the client is ultimately trying to do, then pick the answer that serves it.
Stephan's note: When I interviewed candidates later, the same pattern showed up live. Candidates who restated the client's goal before analyzing anything almost never solved the wrong problem.
A worked example in the same style
Here is a new example built on the same principle.
Case: A regional cycling shop chain has seen flat revenue for two years. The CEO proposes offering free bike servicing for the first year with every new bike sold. She says: "Our service workshops are half empty on weekdays. If buyers come back for free servicing, they will see our accessories and clothing, and our staff can build a relationship with them."
Question: Identify the CEO's primary objective with the free servicing offer.
- A. Reduce idle time in the service workshops
- B. Increase the number of new bikes sold
- C. Increase repeat visits that lead to additional purchases
- D. Reduce the cost of servicing per bike
Worked answer: C. Option A is a side benefit she mentions, and D is unrelated. B is tempting because the offer is attached to new bike sales, but her reasoning focuses on what happens after the sale: buyers return, see accessories and build a relationship with staff. The objective is repeat visits that turn into additional purchases. A strong candidate answers this in about 90 seconds by underlining the "if... they will" sentence.
Test-day tactics
- Answer everything. The PST had no penalty for wrong answers. Solve also scores outcomes, so leaving a task unfinished costs you.
- Bank time early. Easy questions should take under 90 seconds so harder ones get three minutes.
- Flag and return. Mark uncertain answers and revisit them if time allows.
A reader once wrote to me that after working through my practice material he finished his PST with about ten minutes to spare. That margin came from the habits above, built through timed repetition.
How to practice these skills now
Train with full timed sets, then review every mistake by type: reading, math or objective. The Second Key to the PST gives you a second full 26-question written-case test with fresh business cases and a complete answer guide. It was built for the PST format, which is retired, and it remains useful drill material for exhibit reading and calculator-free math. See the Second Key to the PST page, and pair it with the original sample set and a 4-week practice plan. For what McKinsey uses today, read the McKinsey test in 2026.
Frequently asked questions
How long did you have per question on the McKinsey PST?
About 2 minutes and 18 seconds: 26 questions in 60 minutes. Some offices reportedly allowed non-native English speakers extra time.
Should I read the whole case before looking at the questions?
Skim the case introduction for context, then read each question before the detailed text and exhibits. This tells you which numbers to look for and saves several minutes per case.
What is the most common mistake in written case tests?
Choosing an answer that is true or sensible in general but does not address the client's specific objective. The second most common is a unit or decimal error in the math.
Do these techniques help with McKinsey Solve?
Yes. Solve games present a body of information under time pressure and reward candidates who filter for relevant data, reason in a structured way and calculate accurately.