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How many doors in your own country ( Exclude Vehicle door )

Anonymous A

Real interview question. Just want your view how to answer this kind of question.


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Ray replied on 10/03/2017


Thanks for the question. I would clarify with the interviewer that these doors are for people to enter/exit buildings before approaching this problem. There are other types of doors out there which could potentially need to be considered if you do no clarify this (e.g. doors to toy houses, doors to open containers etc.) Here is how I would approach this:

Total no. of doors in my country = (1) no. of dwelling doors (e.g. houses or flats) + (2) no. work-related buildings doors (e.g. offices, power plants etc.) + (3) no. public buildings doors (e.g. museums, art galleries, schools etc.)

1. No. of domestic doors = (Population / average number of people per dwelling unit) x average number of doors per dwelling

  • You can look to further make distinction within average number of doors per household - this can depend on flats/houses (e.g. I would assume flats have fewer while houses have more such as garage doors), or similarly rural/urban dwellings

2. No. of work-related buildings doors = (Working polulation / average no. of people on one flat level) x average no. of doors per flat

  • The problem with this is you need to start somewhere on how you can assume average no. of people on one office flat. I think I'll assume from experience of working in a large global company, one level will host roughly 100 people
  • Once again, if asked to be more thorough, you can break average no. of people on one flat level out into small, medium, large companies to provide sufficient detail
  • Furthermore, you can segment layout of offices into open space and traditional conservative design (e.g. open space will obviously have fewer doors)

3. No. public buildings doors = Similar approach to (2) - For example, you can estimate those going to school and how many schools there would be

I think for this estimation question, the important thing is to be aware that in calculating the number of doors in a given country, you must be rather exhaustive in considering most, if not all possible available door categories. For my suggested answer, I would actually add in an approximate 10-20% at the end of the final answer to account for other types of doors which do not fall under the above 3 buckets (e.g. doors that have recently been manufactured and are in stock etc.)

Hope this helps and I'm happy to hear any suggestions and feedback. Thanks.


Abhilash replied on 10/06/2017

Hello Sir,

My answer to question would be somewhere in Billions . Since India's poluation is 1.25 Billion people. An average 1 bhk would have 3-4 doors . The number of house holds in India would be around 248,408,494 and the average hould size is 4.8.Since most of the Indian population is poor . So lets take on average there are 4 doors for 248,408,494 houses .Then total would be 99,36,33,976. Approxiately 1 billion doors.

But there is huge disparity between the lifestyle of the people so obviously rich has more houses than poor the number of doors per house would differ .If poor has 1bhk and middle class has 2bhk and rich has 3 and 4 bhk . On assumption lets take 2bhk as best possible figure . number of doors for 2 bhk = 6 . Total doors to house holds =1.490450969 billions.

Sinces there are different doors like office doors, other commercial and public building doors , vehicle doors , doors for sale . Doors being manufactured daily . Daily hundreds of doors would be destroyed . The figure would be fluctuating . the figure would definitely go to 2 to 2.5 billions.


List of countries by number of households . https://en.wikipedia.org/wiki/List_of_countries_by_number_of_households

Standard of living in India. https://en.wikipedia.org/wiki/Standard_of_living_in_India

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