Mckinsey Quantum Black SWE Interview

Hey there,

I just helped another candidate who was prepping for the PSS + TEI. It might be slightly different depending on the role (e.g., SWE vs. Data Analyst vs. Research Analyst), but it essentially worked this way

1. PSS is a short, simpler version of a case adapted for your profile. You'll be presented with a situation (e.g., a tech stack upgrade at a client, or an internal data project) and you'll be asked to present how you would structure your analysis, what you would do, etc. It can definitely be less formal than a standard case for a Business Analyst (i.e., more conversational, with a shorter prompt, essentially a series of questions on "how would you do X in setting Y" vs. the "Our client is X and they need to solve Y" template).

My suggestion is practicing on tech-related cases from Preplounge or from the MBA casebooks to make sure you internalize the communication style of the standard McK interview (e.g., how to structure problems, how to give layered qualitative answer, how to manage potential sizing questions, how to communicate with "hypotheses"). 

We can't exclude you might be given a more standard PSS (i.e., closer to a standard case) if your first PSS was more tech-oriented, or a PSS with a sizing/math component. I would just try to do 1-2 simple market sizing cases with a McK alum from your network or a coach.

2. The TEI is the standard interview where the recruiter/consultant wants to dig deeper in your career to understand how you handled challenging situations in the past (helpful video from McKinsey's official YouTube channel below. The preparation is similar to PEI (e.g., build 6-7 stories, use the STAR framework, ensure that your answers can show a spike as McKinsey is obsessed about spikes), but you have to find technical situations where you used your problem solving and context awareness to solve technical problems or to find smart solutions.

It's important you prep by writing down your stories with the STAR framework and, ideally, by checking how they sound to a McK consultant (e.g., you can ask a McK alum from your network or a coach).

Hope this helps!

Tom

Congrats on clearing the early rounds. Quick view on each.

Lightning Talk (Project + PEI). Pick a project with real technical depth. Cover problem, approach, key trade-offs, results, and what you'd do differently. Keep it to 5 to 10 minutes. Be ready for deep follow-ups like "why X over Y" and "how would this scale to 10x users." PEI questions here usually focus on collaboration and ownership.

Problem Solving Scenario (TEI). This is system design plus engineering judgment. Expect open-ended problems like "design a system to handle 1M events per second" or "architect a data pipeline for a recommendation engine." Practise standard system design patterns. Be conversational, talk through options and trade-offs out loud. Common topics include deployment, scaling, latency, data quality, and serving real-time models.

PEI Leadership. Prepare one strong leadership story. Use structure, headline, situation, actions, impact, reflection. Show "I" not "we." Be ready for follow-ups like "what was the hardest moment" or "what would you do differently."

Show curiosity and enthusiasm throughout, QuantumBlack hires people who love solving complex problems.

Good luck.

hi Rid! 

Lighting talk is simple. They want to see whether you can explain a project cleanly, why it mattered, what you built, and how you worked with others. The PEI part is classic: one story about ownership, teamwork, or solving a tough problem. Keep it concrete and linear.

PSS + TEI is usually a mix of engineering judgment and structured thinking. Expect questions like how you’d design or deploy a feature, how you’d debug a system, how you’d handle scaling, or how you’d choose between two architectures. It’s not a full system‑design round; it’s more about how you think, how you break problems down, and how you communicate trade‑offs. They may also ask how you’d collaborate with data scientists or product teams.

The final PEI leadership round is about how you handle conflict, influence people, and take responsibility. One strong story is enough if you tell it clearly.

Alessa