The McKinsey Blogs Wiki. This is a compilation of blogs by alumni and current firm members. I’ve mentioned Marquis’ blog before as a great resource for aspiring consultants, but the others are worth a browse and cover a broad array of topics – from entrepreneurship to healthcare to potpourri.

This post continues my Core Articles series. You can read my previous post on Case Studies 101

Sizing questions are tough. They can be ambiguous, complex, and you’re expected to present a sound solution with minimal data. The following are examples of sizing questions:

• “How many rounds of golf are played in the U.S. annually?”
• “How many baseballs would fit into a Boeing 747?”

To master sizing questions, three skills are needed:

1. Concise, clear note-taking
2. Facility with numbers, units, and back-of-the-envelope calculations
3. Constant, live communication

What follows are the top 10 steps you must take to master those pesky sizing questions and impress any interviewer.

At the beginning…

1) Ask for 30 seconds to 1 minute upfront to gather your thoughts. Take this time to sketch out an early course of action and generate interviewer questions to clarify what’s being asked

On numbers and calculations…

2) Round your answers at each step. If a calculation results in 101 golf balls, use 100 golf balls for the next step. If your answer is $8200, use $8000. This will minimize future mistakes and communicate to the interviewer that you know what you’re doing. As long as rounding doesn’t change the answer by more than 10%, proceed.

3) When you need to make numerical assumptions, pick friendly numbers (eg, 5, 10, 25, 50, 100, etc). For instance, if you need to estimate the percentage of people in the U.S. that play basketball, it’s better to assume 5% than 7%.

4) Clearly label units when taking notes. Don’t get units confused – it’s one of the most common mistakes in sizing questions. Don’t end up with an answer for the average calls/hour/user when the interviewer is actually asking for the average minutes/user/month. Yikes.

5) Avoid numerical ranges. If the question is “How many baseballs would fit into a Boeing 747?”, don’t start your thinking process by saying “First, I’d estimate the volume of a 747 to be between 10,000 and 20,000 cubic feet”. Stick with one number. Ranges provide unnecessary complication and will double the number of calculations.

6) Use a “sniff test” for each calculation. If the answer doesn’t feel right, communicate that doubt with the interviewer (eg, “The answer seems high to me”). Double-check assumptions and steps taken. If it still doesn’t feel right, it’s ok to move on, but make a note of this potential problem area.

On structuring and communicating…

7) It’s ok to communicate doubts and mistakes. If you mess up, here’s what to say:

“Hmm…something here’s not adding up right. Is it ok if I take a few steps back and rework my calculations?”

OR

“Hmm…this answer doesn’t look right. Do you think XYZ is too aggressive an assumption?”

You can insert any question in lieu of “too aggressive an assumption.” The key is that you’re not just asking what you’re doing wrong, you’re hypothesizing on the source of the error.

8) Read interviewer body language. As you’re communicating the steps taken, it can be easy to focus solely on your notepad and calculations. Periodically look-up to see how the interviewer is responding. If they have a quizzical look, it’s ok to continue, but again, make a note that this may be a problem area. If they’re nodding consistently, you’re in good shape.

9) Communicate each step clearly and concisely. Case studies and sizing questions are as much about communication skills as they are about problem-solving skills. What value is a great solution if you can’t persuade the client to implement your recommendations?

10) Don’t over-complicate the solution. In an attempt to impress the interviewer, applicants will often add unnecessary steps that lead to mistakes. Only complicate your solution when it leads to a qualitatively better response. Here’s an example:

If the question is “how many bottles of wine are consumed annually in the U.S.?” – separating wine consumers into an active consumers group (drink a glass everyday) vs a casual consumers group (drink a glass every week) is correct and makes a qualitative difference. Further segmenting into male vs female active consumers and male vs female casual consumers is an example of over-complication.

Thanks for reading! If you’re new to Management Consulted, here are some recommended posts: The Consulting Industry 101; Investment Banking vs Management Consulting; Day in the life of a Management Consultant; Overview of the recruiting process; The Management Consulting Dictionary

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I’d like to thank Mergers and Inquisitions for their kind word. Brian, the author of the site, is a good friend of mine and was the role model for the launch of MC. If you’re serious about finance (and broader recruiting issues), check out his site. I’ll be writing an in-depth post about the projects he’s working on in coming weeks, and hopefully we’ll have a few joint ventures in the works as well

This post will be short. I’m following it up with a post on “Getting a consulting job from a law background” so stay tuned.

There are many valuable consulting-related resources on the web. I want to point out a few:

• From the Killer Consultant – “You got the offer, now what?” – some great tips on how to assess the offer and manage the process
• From the Corporate Whore – “Summer Intern Rules – Don’ts” – a few funny but informative tips for prospective (and current) summers
• Razume – a new resume review service. Interesting concept but not sure how they incentivize reviewers. Thought I’d pass it along – if anyone tries the service (it’s free), let me know your experience!
• From Steve Shu’s blog – “Client Facilitation Skills” – I’ve followed Steve’s blog for sometime now. He writes infrequently, but his posts are always insightful and provide more detail than any other blog I’ve seen on the consulting life

I’m starting a series of interviews with current and prior consultants. This will be great for readers because they’ll get an inside view of topics ranging from what it’s like to work in international offices to cultures of specific firms (eg, Bain, Oliver Wyman) to what ex-consultants are doing now

If any of my readers are interested in being interviewed for Management Consulted, please let me know!

Thanks for reading! For more background info and if you’re new to Management Consulted, here are some recommended posts: Management Consulting and the Consulting Industry 101; Investment Banking vs Management Consulting; Day in the life of a Management Consultant; Overview of the management consulting recruiting process

Subscribe to my RSS feed here to learn more about management consulting jobs.

I offer resume editing and interview prep. I’ll help you stand out from 1000’s of other applicants and land consulting jobs