Hi Anonymous,

In general there is no right or wrong way to do this calculation. It really depends on 1) the situation and 2) your communication (yes, really).

ad 1) Let's assume you need to compare 3 different options and all 3 of them have rather similar numbers. In this case it won't help you a lot to do a rough estimation, because if the numbers are very close from which you start, an approximation won't give you the exact order of those 3 options, so you would miss the whole point of this comparison.

In other words, if a ballpark number is good enough to proceed further in the case and know which direction to go, an estimation is perfectly fine. Sometimes this is difficult to judge from the candidate's perspective - whenever in doubt just ask the interviewer if he is fine with that estimation!

(Unless I have doubts in general that you are comfortable with numbers and want to ensure that you can do math - in this situation I will nevertheless push you to do it accurately. Yes, some shortcuts exist, but it's also possible to do it rather quickly on paper without shortcuts, just a matter of practice.)

ad 2) The actual calcuation is one thing - the exact way how you communicate it is another thing. It's definitely a relevant mistake to answer this mathematical question by doing an approximation and then present it just as the solution to this math question, without mentioning your estimation. So be very explicit in the way how you calculate the number and ensure that the interviewer is explicitly aware of that.

Hope that helps - if so, please be so kind to give it a thumbs-up with the green upvote button below!

Robert