12 Tips for Nailing the Guesstimate Question

AS WE found out in the previous post, the guesstimate question is a usual type of question that you can expect to be asked when interviewing for a position at a consulting firm.

Here are 12 tips to help you nail the guesstimate question:

  1. Practice: We live in a world where most of us use a calculator or computer every day and it can be easy to forget how to do basic arithmetic in your head. Practice doing some guesstimate questions before the interview so that you are prepared. It is a good idea to bring a pen and paper to the interview to keep track of your calculations.  The Vault.com has also suggested bringing graph paper to the interview so that you can graph your results.
  2. Know some basic facts: It will help to know a few basic facts to give you a starting point from which to make reasonable assumptions. It is a good idea to know some key country and city population estimates.  For example, estimates for the population of the world (7 billion), America (300 million), Australia (20 million), New York (20 million), Sydney (4 million) and Melbourne (4 million).
  3. Use round numbers: You are responsible for doing the calculations so pick numbers that are easy to work with. For example, estimate the population of America as 300 million not 309.3 million.
  4. Get into character: An easy way to calm your nerves and improve your performance is to role play. You are not a university graduate desperate for a consulting job, you are a professional consultant. Game on!
  5. Take a moment: It is important to maintain your composure so before starting to answer the guesstimate question take a moment to consider your approach. You can buy yourself some time by saying, “That’s an interesting question” and then pausing to think.
  6. Have a clear approach: It is important to have a clear approach to help you answer the question.
  7. Ask questions: Your interviewer may be able to provide you with direction. If the question is “How many ping-pong balls will fit inside a 747?” the first question you might want to ask your interviewer is “What is the volume of a ping-pong ball?”
  8. State your assumptions: The interviewer may not know the answer or may not want to give you direction so you’ll have to make assumptions.  It is a good idea to clearly state your assumptions. For example, “let’s assume that the diameter of a ping-pong ball is 4cm. The formula for the volume of a sphere is 4/3.pi-r^3. The volume of a ping-pong ball would therefore be about 11-pi centimetres cubed”.
  9. Think out loud: The interviewer is trying to assess your thought process in getting to the answer, not the answer itself. If you don’t think out loud, you make it difficult for the interviewer to give you points.
  10. Explain your logic: As you make your way through the problem it is helpful to explain the logic behind each of your assumptions. Instead of saying “a 747 is about 100 metres long” you could say “I know that  an average car is about 5 metres long and based on my experience I would say that 20 cars lined up end to end would be about the same length as a 747. So I will assume that a 747 is 100 metres long”.
  11. Answer the question: After doing all of the calculation remember to answer the question that has been asked.
  12. Be prepared for the follow-up question: After you answer the guesstimate question, you may be asked “If you had to find the real answer to the question, how would you do it?” This is a test of your creativity and resourcefulness.