Sizing Questions

New answer on Apr 30, 2020
5 Answers
Anonymous A asked on Apr 10, 2020

How would you approach question like this?

How many times will the elevators pass the 12th floor in your office building every day?

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This is a really nice question to be answered. After asking if you can consider a standard working day without any seasonal or weekend effect to be considered, my approach would be the following:

  • Ask or estimate the total number of floors, F
  • Ask or estimate the total number of people working in the office, P (ask if you can consider as even distribution between the floors)
  • Estimate the average number of people that are inside the elevator together, N
  • Estimate the how many times a single person can use the elevator in a day , C (remember to consider also the return way for each person)
  • Total number of elevator calls = P * C / N
  • Estimate the probability of going to a specific floor giving a weight to each floor (e.g. you can use 1 for a standard office and 3 for a floor where there is a coffee area. Remember to consider also the people distribution if you can not consider it even between the different offices)
  • Calulate the probability of going to 12th or higher floors, X. You have to multiply the number of floors >12 by their "weights", and then divide it by the total number of floors multiplying thei weights.
  • Times that elevator passes = X * Total number of elevatore calls

Does it make sense?

Feel free to text me if you want to discuss it futher.


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Anonymous B on Apr 13, 2020


More than a sizing question, this seems to me like a brain teaser.

The key thing here is to see how many floors does the building have above the 12th floor (e.g., only count what goes from 13th floor up). Everything else does not make sense, and precisely for this I would not follow the approach of calculating # of people, verage trips, etc. It would be flawed.

Only for those floors from the 13th up, I would estimate:

  • Total number of people
  • Average times they go below the 12th floor, for which you need data like:
    • Where the cafeteria and leisure spaces are located
    • Where are the meeting rooms located

Hope it helps!



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Best is if you come with a proposal for how you would structure this problem and then we can provide you with feedback. I'll give you some clues:

  • Type of building (residential, office, hotel, mixed purpose)
  • Total number of floors - minus 12 floors
  • How many people in each floor on avg.
  • Number of rides taken by people staying in the floors per day
  • How many visitors per person on each floor per day (meetings, couriers, maintenance)

Hopefully, that helps!


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I think that the first questions would be: In which day of the week? Are we interested in the number of stops or passages at 12th floor ?

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Luca gave the best answer


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