Mental Math Expected in Case Interviews

Question:

Thank you so much for your online tutorial sessions. They are by far the best resources that I have come across so far in terms of case study prep.

I will also be purchasing your "Look Over My Shoulder®" program very shortly and am excited to see what that entails.

I did have a question regarding the level of mental math that is expected during case interview sessions. While I am comfortable with percentages, multiplication, etc., I tend to get a little lost when trying to figure out cannibalization rates, market share percentages, etc., in my head.

#1 - Are these types of items usually associated within case interviews?

and if so,

#2 - Can you use a "back of the envelope" approach when solving? You had mentioned that you won't get full points for using this method in simpler calculations but was wondering what exactly "simpler" means!

My Reply:

Rule #1: Get the math right.

Rule #2: See rule #1

If you can do the math in your head and do it accurately, that's of course the best scenario.

If you need to use a piece of paper, by all means use it. Better to use paper and get it right, then to use your head and get it wrong.

The expectation at the Top 3 firms is a little higher. So if the interviewer can do the math in his/her head and you need to use paper, that looks a little weird. But if you nail the rest of the case, that is forgotten pretty quickly.

At other firms, if you need to use paper, that's not a big deal. I had one interview at a boutique where the interviewer just gave me a calculator before the interview even started.

By the way, most of the math is multiplication and percentages. The others are less common, but still possible. Many times the math is not planned, it just seems to be an appropriate thing to do, given the context of the conversation.

For more materials on preparing for a case interview, review my free video series on Case Interview Secrets .

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