Consulting Interview Math

5khj's picture
Rank: Senior Chimp | 21

This topic has been addressed many, many times, but always in scattered places. And I also get differing stories. So, I thought it might be best to start a thread in order to discuss peoples' experiences / perceptions of the math questions in MBB-type consulting interviews in one place .

Some people say the cases generally involve really straightforward math (calculate the margin, profit, etc.) -- arithmetic with large numbers, basically.

I've heard other people say the math questions can be pretty complex.

The only consulting interview I've had so far involved a pretty qualitative case interview, so I haven't had a real taste of data-based interviews.

What are your experiences?

Comments (17)

Jul 23, 2010

It's all math you should be able to do in your head or with a few quick scribbles. If you're doing long division you've screwed something up. They won't be asking you to do integral calculus or anything.

Jul 23, 2010

I'd add that you should be carefully writing out the major steps in your calculations so that you can keep track of what you are doing.

Yes, the math is arithmetic... but you are doing it under timed conditions in front of an interviewer for a job. You will be nervous and prone to make mistakes.

Additionally, it is easier to keep track of what you are doing if you are writing out the steps as you do them.

Finally, it is MUCH easier to explain you calculations if you are writing them out.

Make sure to speak slowly and clearly. Be methodical and take your time.

Jul 23, 2010

my advice would be to get quick at doing percents. Specifically, be able to get the multiples of 10 and 5 down...for example: What's 65% of 21,000?

You should be able to do that in your head.

Jul 25, 2010

Alright well the next question is: How fast do you have to be able to do these things? Are you allowed to actually write your calculations down (I assume so, according to vyger's comment), or do you need to be able to rattle them off in your head? Or are you just saying you should be able to do it in your head in order to move things along quickly?

Jul 26, 2010

"Okay, so we need 65% of 21,000. Well, let's round 65% to 2/3rds - it's within a couple percent. Two thirds of 21,000 is 14,000."

The expectation is that you can talk fluently through math like that. The problem comes when you mess things up, or when you do something like this:

"Okay, so we need 65% of 21,000..." [interviewee writes furiously for a silent minute] "Okay, 13,650."

Jul 26, 2010

^^^ that works (the 2/3rds part)

BUT, you can also impress interviewers by doing these calculations quickly and painlessly (if you are comfortable with this). I think of it as 60% of 21,000 is 12,600, and 5% of 21,000 is 1,050, add those together and you get 13,650. You really wouldn't need to write anything down other than your final figure, and that shouldn't take you more than 5-10 seconds.

Again, that is only if you are comfortable, the 2/3rds part works perfectly well and at the end of the day it is the big picture that matters with these companies. And to be honest I've lost some interviewers before with doing too much quick math...that didn't go too well.

Jul 27, 2010

I found that it helps to talk through the math out loud as you do it methodically on the paper. Helps engage the interviewer and also makes sure you stay on track and catch errors.

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  •  Jul 30, 2010

As in the rest of consulting, I think it's all about breaking the problem down in a way you can understand it, and in a way that you can explain well. So that works for the 2/3 approach and the 60% + 5% (how'd you do the 60%?) approach. To me, it seems most intuitive to break 65% into 50% + 10% + 5% (10,500 + 2100+ 2100/2). All easy to calculate. But yeah definitely talk through everything.

Jul 30, 2010

I'm an MBB interviewer. Define "rusty". Are you just a bit slower than you'd like to be, or are you unable to identify what it is you're supposed to be doing in a given situation?

Jul 30, 2010

Check out calculation rankings

Jul 30, 2010

unless you're explicitly applying for a quant position at that fund it's likely going to be just brainteasers and basic probability theory. go through the respective sections in 'heard on the street' (crack), 'quant interview questions' (joshi) and 'practical guide to quant. fin. interviews' (zhou) and you'll be fine. I found zhou's book the most helpful. that being said, they'll probably also ask some more technical stuff that's related to what they do.

Jul 30, 2010

I like the math app Kopfnuss.

Jul 30, 2010
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