How to handle a math mistake

Case Interview
New answer on Aug 01, 2022
9 Answers
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Anonymous A asked on Jul 28, 2022

Hi everyone. I find that I am good at catching my own mistakes in the math section of case interviews. However, I feel like I communicate/handle it a bit awkward as I am not sure what to say that is graceful and confident. How do I tell an interviewer that I know I made a mistake and would like to fix it? 

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Hani
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replied on Jul 28, 2022
Consultant at Oliver Wyman | Ex-Strategy& and Booz Allen | 3+ years in Consulting Experience in the Middle East

Hi there,

First, you're doing a good job double-checking and finding a mistake - this is a very good habit to build. 

It is significantly better for you to catch your own error and notice it rather than to have the interviewer point it out - the interviewer will be asking himself/herself whether or not you can be relied on the job to do quick and accurate work (not expect you to be perfect but if you do a mistake they wanna know that you will be able to catch that mistake and fix it on your own proactively).

The best way to deal with this kind of situation (ideally not be in it in the first place) is to be transparent and honest - acknowledge the error immediately and redo the calculations recalculate (the interviewer most probably noticed the error as he has given this case +20 times). Once you've done the calculations and have the correct answer simply restate it confidently and move on to the rest of the case, do not feel the need to apologize excessively or be embarrassed by the fact that you made a simple math error (many candidates get caught in this trap and end up blowing the whole issue into a much bigger deal than it needs to be) just recognize that everyone can make a simple error occasionally and it is really not that big of a deal.

There are no phrases to memorize for this you can use simple communication “just let me double check the number quickly, it seems there was a minor issue with the math the answer is actually B and not A (you can also add the reason of the mistake if you feel like it”

Remember a math error alone will not tank your interview. In fact, it might be a good opportunity to show how you can bounce back strongly and show your resilience.    

Hope this was helpful!

Best, 
Hani 

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Ian
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replied on Jul 28, 2022
MBB | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

Hi there,

Love what the other coaches have said.

Basically, don't sweat it. You've caught the mistake which is a good thing! Just say “ah, just need to adjust x to be y”. And move on! That's it :)

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Moritz
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replied on Aug 01, 2022
Unearth your spike & get the offer |ex-McKinsey | 120+ coachings & interviews @ McKinsey | ESADE MBA | Transition Expert

Hi there,

It's hard to guide people on how not to be awkward. 

Fundamentally, you have no reason for it. Catching a mistake is a very good thing to do in an interview and is very close to real life, where the final deliverable is always polished but the way there is paved with all kinds of mistakes. In my opinion, it's a non-issue because a bit of awkwardness is very forgivable in comparison to a math mistake that isn't corrected.

And if you ever do miss a mistake that the interviewer needs to correct, make the corrected number, equation, etc. your own and run with it confidently. Again, very close to real life where people help each other out by spotting each other's mistakes, which is perfectly fine. I always thought highly of candidates that didn't crumble when that happened and showed some mature  attitude.

Hope this helps a bit. Best of luck!

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Clara
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replied on Jul 31, 2022
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello!

Something I always tell my coachees is that IS NOT ABOUT NOT MAKING MATH PROBLEMS, we all make them at some point, but about knowing how to not let this sink your interview. 

Often times, is not the mistake itself, but the way it affects the interviewee, that gets blocked completely and looses the case from then on. 

There are a few techniques to implement, that for me are musts in order to successfully interview - since, as we said, everyone makes mistakes, and even more the day of the interview in which you are very nervous. Feel free to reach out!

Hope it helps!

Cheers, 

Clara

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Udayan
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replied on Jul 29, 2022
Top rated McKinsey Case & PEI coach/Multiple real offers/McKinsey EM in New York /6 years McKinsey recruiting experience

The thing that gets lost when preparing for interviews is that they are testing for skills you would bring into client situations as a consultant. There are many occasions where you'll have to revise your work based on new information and it will be a little challenging to communicate it to the client but it is the best thing to do. 

Similarly, apply that logic here. You made a mistake, it happens. Own up to it, say that you realized you made an error and would like to go back to fix it (assuming that this is before it is pointed out to you). Most interviewers will be happy about you handling the situation in a calm frame of mind. 

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Sofia
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replied on Jul 28, 2022
McKinsey San Francisco | Harvard graduate | 5+ years of coaching | DISCOUNTED SESSIONS Sep 2022 | Free 15 min intro call

Hello,

Don't worry about this too much - the key is that you caught it and corrected yourself. Something like “oh, actually X should be Y because of Z” conveys that you have caught the mistake and understand why your initial answer was wrong. It might feel a little abrupt, particularly if it has been a little time since the mistake was made, but that's ok! Just point it out quickly and continue with the case.

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Francesco
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replied on Jul 28, 2022
#1 Coach for Sessions (4.000+) | 1.400+ 5-Star Reviews | Proven Success (➡ InterviewOffers.com) | Ex BCG | 9Y+ Coaching

Hi there,

Q: How do I tell an interviewer that I know I made a mistake and would like to fix it? 

I guess you are catching the mistake when you do the double-check.

I don’t think you need a very specific script.

Something like “Let me do a quick double check.. actually I think there was an issue with the math here, it should have been X and not Y” should work well.

Hope this helps,

Francesco

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Florian
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replied on Jul 28, 2022
#1 rated McKinsey Case and PEI Coach | 5 years at McKinsey | Mentorship Approach | 120+ McK offers in 18 months

Hey there,

As with everything else in a case interview 

  1. Be transparent
  2. Overcommunicate
  3. Don't overthink it
  4. Don't stress

You know what, I just figured that these numbers do not make any sense. Let me just get back to my approach/calculation to fix it. I'll be right back with you.

Cheers,

Florian

 

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Cristian
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replied on Jul 31, 2022
#1 rated and most recommended McKinsey Coach | 97% success rate (tracked) | Honest feedback: no sugar-coating

Hi there, 

Making small mistakes is not a big deal. So just think of it as being not a big deal. If you happen to make one, try to re-adjust quickly, be open about it to the interviewer and move on. Consultants also make mistakes in real-life - what makes the difference between the good and bad ones is how elegantly they recover.

Best,

Cristian

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Hani gave the best answer

Hani

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Consultant at Oliver Wyman | Ex-Strategy& and Booz Allen | 3+ years in Consulting Experience in the Middle East
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