Scientific notations to ease calculation

Calculation tips Case Calculations Scientist Background
New answer on Mar 23, 2020
7 Answers
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Anonymous asked on Mar 15, 2020

Dear Preplounge community,

I'm preparing for strategy consulting interviews, coming from a scientific background. As many people I struggle to do calculations including many 0s by hand.

I saw many times the trick using K as thousands, M as millions and B as billions, however I found the scientific notation to be more clear and easier to use. Calculation with Ks, Ms and Bs can still include many mistakes while the scientific notation includes a simple addition.

As I never saw the use of the scientific notation as a tool advised, I wonder if it can be frowned upon in consulting interviews, or if it's okay to use.

If the reason is it's not client-friendly, I still prefer use it in my head and convert it in thousands/millions/billions than using K, M, B.

As an example:

45 millions * 250 = (45E6 *2.5E2 = 112.5E8 = 11.25 E9) = 11.25 billions, the part in parenthesis being in my head or on paper and 11.25 billions what I present.

Best regards,

Clément Camus

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Daniel
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replied on Mar 20, 2020
McKinsey / ex-Interviewer at McKinsey / I will coach you to rock those interviews

Hi Clement! you can definitely do that, as long as you arrive to the right answer nobody cares how you calculate it.

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Luca
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replied on Mar 16, 2020
BCG |NASA | SDA Bocconi & Cattolica partner | GMAT expert 780/800 score | 200+ students coached

Hello Clement,

The first and most important objective that you have during your interview is to not do any mistake with your calculation.
Every time that you are asked to do some calculations that you have to:

  1. Explain what you are gonna to calculate
  2. Ask for some time
  3. Do the calculation on a separate sheet
  4. Present the result

The interviewer does not care about your calculation methods as far as you don't do any mistake. That means that you can use your scientific notation and then you can change the format to make it more client-friendly.

Hope it helps,
Luca

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Clara
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replied on Mar 15, 2020
McKinsey | Awarded professor at Master in Management @ IE | MBA at MIT |+180 students coached | Integrated FIT Guide aut

Hello Clement!

What you wrote in your post not only makes sense, but it´s actually one of the exercises that I make with my coachees when tackling math-intense business cases.

Keep it up, it totally helps when having big numbers.

There are other techniques that you can try: for instance, when you will have to do multiple calculations, lay out all the different steps you need to do and, instead of doing them in pure "order", seeking for more favourable orders based on numebrs that are easy to operate among them.

Hope it helps!

Cheers,

Clara

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Sidi
Expert
replied on Mar 15, 2020
McKinsey Senior EM & BCG Consultant | Interviewer at McK & BCG for 7 years | Coached 350+ candidates secure MBB offers

Hi Clément! This is totally fine. The notation has nothing to do with client friendliness. The only two things that matter are

  1. You are rock solid in coming up with the correct result based on your notation
  2. You are able to take along the interviewer on each actual operation (NOT side calculations!)

So in your example, you say: "Okay, so in order to compute XYZ (i.e., the metric that you are actually calculationg, for example number of units sold per year) we need to multiply 45 million daily units by our assumed 250 business days. Let me quickly do this."

[then you do your notation and written calculation]

--> "Okay, so with 45 million units per day and 250 business days, we can expect 11.25 billion units in a full year. Let's see what this actually means in the bigger context...".

Cheers, Sidi

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Antonello
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replied on Mar 23, 2020
McKinsey | MBA professor for consulting interviews

Hi Clement, I definitely recommend it :)

Best,
Antonello

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Francesco
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replied on Mar 16, 2020
#1 Coach for Sessions (4.000+) | 1.500+ 5-Star Reviews | Proven Success (➡ InterviewOffers.com) | Ex BCG | 9Y+ Coaching

Hi Clément,

it is totally fine to use scientific notation for math in a case interview if that helps you to decrease mistakes and increase speed. I would also recommend the following steps to improve on the way you solve math problems in cases:

  1. Repeat the question – candidates sometimes do mistakes answering the wrong question in the math part
  2. Present how you would like to proceed from a theoretical point of view (you may ask for time before presenting if you initially don't know how to approach the problem)
  3. Ask for time and perform the first computations
  4. Present interim steps to the interviewer to keep him/her aligned – don’t just say the final number
  5. Continue with the computations until you find the final answer
  6. Propose next steps on the basis of the results you found

Best,

Francesco

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Marcello
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replied on Mar 15, 2020
FREE Coaching tailoring | Active Associate @MonitorDeloitte | Interviewer @Monitor@Altran

Clément,

Thanks for your post.

In my experience it should be completely fine to use whichever method you wnt to come up with your answer internally. By that, I mean that if you carry out your calcs in your head or in a scratch paper using the scietific notation it is completely fine.

However, and as you point out, it is key to present anything in the consulting world in the most client/audience friendly way. Remember that good and efficient communication is as important as solid analysis for a consultant. Thus, make sure you always embrace your client/interviewer/audience in the best way for them to unerstand your points, which in this case would be using the business notation (K, M, B).

Hope this helps!

M

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Daniel gave the best answer

Daniel

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McKinsey / ex-Interviewer at McKinsey / I will coach you to rock those interviews
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