Communicating precise math calculations properly

Question

Hey there, i have a question regarding verbal communication during calculations in (virtual) case interviews. I understand that the interviewer should be included in the process of calculation by verbalizing every step of a math problem.

For example, when making a calculation like 23,000 * 50% * 10% + 2,000, i can easily communicate every step with the interviewer („So first, i calculate 50% of 23,000, which is 11,500. Next i calculate 10% of these 11,500, which results in 1,150. Finally, i add 2,000 to these 1,150, which leads us to a final result of 3,150.“)

What i am struggling with is how to effectively communicate (precise) multiplications like „289 x 486“ or dividing numbers like 31/792, and making calculations like 17% of 1,724.

When being asked to calculate these number precisely in a case interview, i would do a written multiplication or division, in which the „intermediate“ results are probably rather confusing to an interviewer.

MULTIPLYING NUMBERS

On my paper, the written multiplication would look like this:

289

486

________

1,734

+ 23,120

+ 115,600

__________

= 140,454

And this calculation takes like 15-30 seconds.

Which of these two would you say is the better approach

(1) „I am now going to do a written calculation of 289 x 486 on my paper an get back to you with the result in 20 seconds? (….do the calculation for 20-30 seconds…). So the result of 289 x 486 is 140,454."

(2) „I am going to calculate 289 x 486 now. To do this, i will split the calculation in three steps: first, multiply 289 with 6. Second i multiply 289 with 80. Third i multiply 289 with 400. I will then add these three results up. So for the first step, my result is (…do the calculation for 5 seconds…) 1,734. For the second step, my result is (…do the calculation for 5 seconds…) 23,120. For the third step, my result is (…do the calculation for 5 seconds…) 115,600. Now to get to the final result of 289 x 486 i am now going to add up these three numbers (…do the calculation for 5 seconds…), which results 140,454. So 289 x 486 is 140,454.

DIVIDING NUMBERS

When doing a precise calculation like 31/792, this always takes me like 20-25 seconds. Here i do not know how to make any useful intermediate results i can communicate to the interviewer? Would you say it would be appropriate to say: „I am now going to do a written calculation of 31 divided by 792 and will get back to you with the result in 20 seconds.“? Or do you have a better idea?

Thank you so much in advance!

Answer 1

Hey there,

I'd challenge the initial assumption that you need to lead the interviewer through your actual intermediate results while you are calculation. It is much more efficient and also easier for most candidates to break the process down into 3 steps.

First, take time to structure your approach and communicate it to the interviewer (''I want to break the calculation into 3 steps, 1.....2.....3......).

Second, ask for time to perform the actual math in peace and quiet (of course, ask if the interviewer is fine with this approach)

Third, communicate your answer to the question top-down; if you want, you could communicate intermediate results and steps here but it is not needed!

A case interview represents a hypothetical client-facing situation with a CEO. The CEO does not care about intermediate results. They care about

Correct logic and assumptions, which you communicate initially
The actual answer to their question; they don't want to be bombarded with irrelevant figures, number, or data

That way you will make sure to have 100% focus and concentration on the math and not split attention to approach, calculations, and communication.

This is a turn-key tip to make many candidates much more comfortable with math and reduce errors by a large margin.

Cheers,

Florian

Answer 2

Hey there!

The first option is more preferable for sure. You do not have to verbalize every step of your multiplication/dividing process. Just do not forget to specify what you are counting and why. It's totally okay to do all of the math in a written format and will be easier for you as well!

For any further questions, you can contact me through DMs!

GB

Answer 3

Hello!

I think you are missing a previous step in which you need to share your thoughts with the interviewer when it comes to the overal approach "I will 1st calculate this, in order to ..."

Then, when it comes to communicating the math, that is quite personal. One important point is that it does not need to be either your point 1 or 2, there is also the chance to do the math in silence and be more proactive in the overall strategy communication.

Hope it helps!

Cheers,

Clara

Answer 4

FALSE: "interviewer should be included in the process of calculation by verbalizing every step of a math problem."

This is wrong! This is a classic misconception that comes from the statement of "talk through your math"

Please do not spell out every single calculation you do! Rather, what should you do?

Verbalize, in general, what you want to do. I.e. what you want to solve for and WHY.
Articulate/lay out the exact math you will do. i.e. "I am going to multiply x by y and subtract by z"
Then go do the math silently. Pop your head up if there are intermediate #s that are calcualted (i.e. if calculating across 3 products, state the total when you arrive at the answer for each individual product)
React to/observe the number. Have a "so what" or implication to the #

Answer 5

Hey, I recently got an offer at Mckinsey. I'll be happy to give you my two cents and do some prep to help you out. Sh... (read entire answer)

Hey, I recently got an offer at Mckinsey. I'll be happy to give you my two cents and do some prep to help you out. Share your profile so I can dm you. Cheers