Ace the Case Interview

How to commercialize the teleport? Penguin population growth rates are increasing. Why is it happening and how it will affect the world?  How many gas turbines are there in Lithuania?

Probably some years ago you did not even imagine that one of these questions could easily pop up during your next job interview. However, the increased job market complexity affected also the recruitment process and today it has become a reality.

At first sight, this is ridiculous, right? Why a stellar business graduate with Magna Cum Laude like you should even care about penguins, teleport or gas turbines somewhere in Lithuania? Being a good student, you spent 5 last years carefully calculating WACC and moving supply and demand curves, and now, when you have finally graduated and applied for your first business analyst job, the only thing the interviewer seems to care about is penguins. Seriously?

Actually, the logical explanation does exist and in this post, I would like to explain the rationale behind case-interviews, introduce the main concepts, preparation tips & useful sources.

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What is the case interview?

Generally speaking, case interview is a specific type of a job interview, in which the applicant is given a question / situation / problem / challenge and asked to resolve it. It is important to understand that case interviews are designed to assess how you deal with the problem and how you reach the solution, rather than on the specific answer you come up with.

Historically, case interviews were used mainly by management consultancy firms – the so-called “renting out brains” business. Young consultants are basically paid for their ability to solve problems,which makes this skill critical.

However, in the reality case interviews check so much more apart from problem-solving skills. They also help interviewers to assess candidate’s ability to think structurally and logically, his numerical and verbal reasoning skills, business understanding and commercial awareness, communication and presentation skills. All these competencies are crucial to succeed in today’s competitive job market regardless the industry.

Many companies have realized this fact and started to adapt their recruitment policies, which made case interviews increasingly common in many other spheres and disciplines. It has been already widely adopted in the financial and tech industries. Also, you can easily get a case study, if you apply for management trainee / leadership development programs in different industries.

Therefore, even if you are not interested in pursuing a business degree or a consultancy career, excelling at case interviews is an extremely useful skill that will definitely boost your overall employability.

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Type of case interviews

Normally case questions fall into one of three major categories: business case questions, market estimation tasks or brainteasers. It is also quite common to find a market sizing question within a larger business case question.

1. Business case questions

These questions test a candidate’s ability to think strategically about problems/opportunities and apply theoretical concepts and common sense to the business reality. There are many different types of cases, however, the following segmentation covers the most common business concepts to be aware of: entering a new market, developing a new product, pricing strategy, growth strategy, starting a new business, competitive response, increasing profits, company turnaround.

• How should our plant deal with waste products?
• How can we double the regional sales of our product – electronic cigarettes in 2 years?
• A friend of yours is considering becoming franchisee of Burgerking and he needs your advice.

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2. Market estimation tasks

A market estimation case interview question or “guesstimate” is one where you’re asked to determine a quantitative variable relevant to the case you are solving. If you have to estimate the size of a market for a particular product, this guesstimate is called “market-sizing”.

Sometimes market estimation tasks are also referred to as “back of the envelope” because of the traditional question formulation: “Imagine you are on an airplane without an internet connection or any books and you need to estimate … on the back of the envelope.”

• How many passengers fly through London Airport in a calendar year?
• How much does the Boeing 747 weigh?
• What is the market size for a cancer diagnostic technology in the U.S.

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3. Brainteasers

Brainteasers require you to answer an unusual or abstract question, developing a suitable answer based on logic, analysis, and hypothesis. These questions are probably the most difficult because it is almost impossible to prepare for them. 

Some years ago brainteasers were used a lot by tech companies, but later Google first admitted that on the hiring side, they are a complete waste of time. Other tech giants seem to agree and in general, nowadays brainteasers are less common. However, it is still possible to get one during an interview because interviewers sometimes want to see how candidates perform under pressure and brainteasers are perfectly designed to test your ability to think quickly and logically under stress.

• At 3:15, how many degrees there between the two hands of a clock? 
• In the Chicago subway system there are two escalators for going up but only one for going down to the subway. Why is that?
• How can you tell if the light inside your refrigerator is on or not?

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General advice

1. Listen & Ask questions

Always keep in mind that case interview is not a one-sided process. Otherwise, it is a two-way discussion.  A successful case-interview, like any other pleasant dialogue, requires encouraging another person to participate and listening carefully.

To involve the interviewer in a discussion – simply ask questions. You can always confirm something or ask for additional information that can potentially help you solve the problem. However, do not ask questions just for the sake of doing it – focus on the most important ones for the case solution (remember, the 80/20 rule or Pareto Principle).

There is no point in asking questions if you are not willing to listen. Therefore, pay close attention to the interviewer’s answer, its implications and even the word choice and manner of speaking that might also lead you down the right path.

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2. Pay attention to your notes

It might be surprising, but the way you take your notes is quite important. It is not only about facilitating your case solving process, but it also demonstrates how you can present the information and make it visual.

Write as neatly as possible (using pencil might help you to avoid mistakes) to make the solution easy to read and understand, use separate sheets for different case sections (f.e. info/structure/calculation) and give page numbers not to get lost in your notes. Also, do not forget to structure/visualize your thoughts using decision tree/tables/graphs/diagrams/scheme when it is relevant.

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3. Structure with MECE

Demonstrating a structured approach to the problem is actually as important as solving it. You need to focus on being structured in everything you do and say: from brainstorming and asking questions to making calculations and providing a final answer.

A structured approach to your case will help you review all possible options and analyze the most likely outcomes while weighing the risks and rewards of each action. Thinking graphically and using decision trees is very helpful to break down the problem into distinct segments that can be further explored through smaller pieces. 

Make sure that all your “tree branches” correspond to the golden consulting principle – MECE, which means “Mutually exclusive” (there are no overlaps between issues) and “Collectively exhaustive” (all high-level issue areas have been covered by the first-level branches of the tree).

• Q: How can I get from Belgium to Spain?
• A1: You can take a flight or take a train. (standard)
• A2: There are 3 ways you can travel: by land, sea or air. If you travel by land, you can take the train, drive a car, take a bus, motorbike, bicycle, or even walk. If you travel by sea, you can sail, take a motorboat or a ferry. If you choose traveling by air, there is the shuttle or a helicopter. (MECE)

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4. Keep frameworks in mind

Actually, probably one of the most difficult parts has already been done for you a long time ago: you can easily find prepared answer structures for the most common business problems. However, sometimes this availability brings more harm than good because people apply these frameworks blindly, without thinking about case specifics and, as a result, they miss the most obvious. Get familiar with all the frameworks and learn how to apply them in practice, but at the same time treat every case individually and adjust the structure accordingly. 

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5. Think first, then think again out loud

Either we speak about the overall case structure, way to calculate something or an answer to a smaller specifying question – always take time to think. It is better to pause for a moment to prepare a structured answer with an explanation of the rationale behind than to say something ridiculous or not exhaustive. Share with interviewer not only your final answer/decision but outline the reasoning and your overall thought process.

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6. Be hypothesis-driven

Start a case with your structure applying the framework, but then right away move to a hypothesis that will drive your analysis further. Develop it as early as possible and do it explicitly, think about information needed to test it. Adjust your hypothesis when you get new data and try to take it to the logical end and get the problem isolated. Your initial hypothesis will most likely be wrong or overly general and it is absolutely ok. Introducing the hypothesis from early on gives your analysis more clarified direction.

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7. Stay focused and  build a big picture

While you are digging into your hypothesis, it is so easy to get lost in the details and forget about the original question. At a certain point in time, it is important to take a small break to summarize your key findings for the moment and their fit with a big picture. Be agile, sometimes you might need not only to adjust the hypothesis but even to reconsider your overall framework.

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8. Think business

Even if you have not studied business earlier and the case question does not have anything to do with economics, you should try to adopt a “business thinking” approach – understanding the complexity of the world by considering the interrelations between players and looking for both direct and indirect implications of each action. Try to connect the dots and move from trend identification to driving implications by asking wonderful “so what” question until you get to the point.

The best way to develop sequence thinking is to follow what is happening in the real world (business related periodicals like WSJ, Financial Times, Economist, business/news related channels like Bloomberg/CNN) and think about the full set of implication (both direct and indirect) caused by a certain event.

• US oil production increased – Drop in oil price – Oil exporting countries have less income (direct) – Citizens of these countries receive less unemployment benefits (indirect)
• US oil production increased – Drop in oil price – Other types of energy are becoming relatively more expensive than oil (direct) – Alternative energy companies reduce their r&d expenses in the new affordable alternative energy solutions (indirect)
• US oil production increased – Gasoline prices dropped (direct) – use of public transport decreases – financial performance of bus manufacturers worsens (indirect)

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9. Do the Math

Making quick and, at the same time, correct calculations is crucial. Very often you need to calculate something in your head and there are many tricks that can help you to excel.

First of all, do not always run for the accuracy – if it is possible, use round numbers to simplify the process. Then, break all the difficult numbers into either tens or halves to do quicker calculations. However, if you are not sure that you can calculate the equation correctly in your head, better to do it in written than to be completely wrong.

• What is 37,5% of 25,000?
• 25,000/10 = 2,500 = 10% of 25,000
• 2,500/2 = 1,250 = 5% of 25,000
• 1,250/2 = 625 = 2.5% of 25,000
• 37,5% = 3 * 10% +5% +2,5%
• 37,5% of 25,000 = 3 * 2500 +1,250 + 625 =9,375

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10. Practice

Practice makes it perfect. The earlier you start, the better. There is a huge collection of literature and practice case-books already waiting for you. But do not get stuck with your books for a long time – practice with other people. You will be surprised how many people are practicing cases every day and how easy it is to find a good partner – share new cases with each other, exchange feedback and grow together. However, be careful with over practice to avoid a mental burn-out and thinking only  in a way limited by earlier solved cases and memorized frameworks.

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Useful sources

Must-Know basics

• Case in Point book by Marc Cosentino – quote from Wall Street Journal: “When in doubt, MBAs turn to ‘Bible'”
• Case questions website by Marc Cosentino 
• Case Interview Secrets by Victor Cheng – very practical hands-on tips
• Case interview preparation videos by Victor Cheng
• LOMS (Look Over My Shoulder) course by Victor Cheng
• Crack the case system by David Ohrvall – a full course of case interview preparation including many videos, tutorials and practice questions
• MBA case website by David Ohrvall
• MConsulting Prep videos 

Case examples

• Ace the Case from Wetfeet
• MBA case library from David Ohrvall website
• Consulting Case 101
• Master the case 
• PrepLounge library
• MBA books – Almost every business school has an annual publication of business-cases and many old editions are piblicly available (on request)
• Consulting company websites (Deloitte, McKinsey, BCG, Bain, ATKearney, Accenture)
• Quora and Glassdoor (real questions, but normally no solution )

Finding a case interview partner

• Case Interview Community: PrepLounge.com
• Case Interview Partner 
• Consulting case 101 partner section 
• Master the case partner section 
• Consulting Clubs within Universities f.e MIT (1,2)
• FB & LinkedIn groups

Maths

• Speed mathematics book  by Bill Handley
• Secrets of Mental Math book by Arthur Benjamine
• Numerical Reasoning Practice Tests book from SHL 
• Case Interview Math 
• Preplounge Mental Math 
• Mconsulting math 
• Master the case math 
• Udemy course on fast math 
• Other  publicly available SHL/GRE maths/GMAT maths resources

Brainteasers

• Preplounge brainteasers 
• Haidong’s Puzzles, Brain Teasers, and Interview Questions  practice slides
• Hard to solve brain teasers practice tool

Thanks for reading and I hope you found this post useful! If you are interested in posts with more detailed information on each type of the case or I missed something you consider important, let me know.

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