Pen and paper - how often to use for mental calcs?

Using pen and paper should help the process of working towards the solution you are presenting in a clear and concise manner. If it becomes an extra step that just slows you down in giving the answer to a short question, it is obviously not very well utilized. Overall, you want to make sure that the interviewer understands where your head is, that you can easily backtrack if needed and that you yourself don't get lost in a potential numbers jungle.

During Covid, there was a time when all interviews were virtual and the interviewer could not even see the candidate's notes. So I don't believe that any firm is strictly set on anyone approach at this point. Be pragmatic and tailor it to the situation. But when in doubt, I would rather write something down for documentation than “juggling” around with numbers and structures

It is absolutely fine to use a paper and pen to do calculations - consulting firms are looking for people who are comfortable with numbers, not for human calculators. That being said, if you're able to do calculations without it, then that's fine too. 

I would be very surprised though if you could get through the whole of the maths part of the case without having to write down, at the very least, the methodology that you're following to solve the question. Write down what you need to write down to keep you on track and stop you from making silly errors.

Good luck! 

I heard smth like this in Europe. First case is favoured in McKinsey, the second in BCG. Don't know about Bain though

Hi there,

there is no preference here.

I would always use pen and paper for the sole reason that you want to have a paper trail of your thoughts and calculations.

If you end up with a wrong result, it gets tedious to go back to your calculations as there is no record of it.

Additionally, you appear more structured AND organized, which also helps with the outcome.

Cheers,

Florian

Hi there,

For quant questions, what matters is you structuring the math right, taking shortcuts and landing on the right numbers. HOW you do that can vary and isn't the core of the assessment. 

Practically speaking, when given a calculation to do, here is how you should deal with it:

1- If the calculation is straightforward and can be done mentally, and if you feel very confident about the answer, you should go ahead and give the answer right away, without justification.

2- If the math requires a bit more structuring and you do not have the answer at the top of your head, do structure it on paper (e.g., decompose, use shortcuts etc.,). If it's a simple structure, no need to walk the interviewer through it, just go ahead and give the answer. If the structure is complicated and takes time to solve, you can walk the interviewer through it to ensure it's correct and avoid awkward silence.

All in all, whenever possible answer the question directly, whenever complicated do write things down.

Best of luck,

Mario

Hi Nick,

It's all contextual. It depends on the case (and, honestly, interviewer).

Let's keep this rule very simple:

1. If you can not take time and solve the problem in a correct, structured, clear way, then don't take time.
2. If you need to take time, because otherwise you will have an incorrect, messy, unclear answer, then take the time you need.

Your question is a false choice :)

Correct answer: they don't care.

They care that you are able to adequately explain your process, and able to perform tasks in an efficient way. 

If they are not able to follow you there's a problem with communication. If you are being too mechanic and “bureocratic” when approaching any problem, then you are not being efficient.

So you have to apply judgement. Good judgement is around the lines of: if you need to formula with more than 3 steps you should write it down. Otherwise you should be able to communicate and calculate effectively without resorting to paper.

Hello,

I agree with the general feedback you have received here - there is no one right or wrong answer. If a calculation is straightforward and you can do it in your head, go for it. If it requires several steps and would be cleaner and easier to follow if you write it out on paper (+ would decrease the chance of you making a mistake), then write it out. Generally most quantitative question that you get in cases will fall under the latter bucket.

I think you can ask many questions to improve your performance, and this is not among them.

You have to use your pen and paper only when is of help to you.