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# interview logic q

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1. What is the number of planes in air at this moment?
I would like to see how you would think about this/attempt it. I don't care how large/small the answer is but the way of thinking.

My try would be to say average plane in every country in the sky now is 15 and multiply it by the number of countries x so 15x
2. (Original post by Daniel Atieh)
What is the number of planes in air at this moment?
I would like to see how you would think about this/attempt it. I don't care how large/small the answer is but the way of thinking.

My try would be to say average plane in every country in the sky now is 15 and multiply it by the number of countries x so 15x
this is an example of a fermi problem / fermi question. googling that term would probably find plenty of examples.

---
I watched a series this summer called 'city in the sky' which had the premise that at any time there are enough people in flight to populate a mid sized city.

so I'd guestimate the population of a mid sized city and divide by the guestimated number of people on a plane.

if you get within an order of magnitude you're doing pretty well - that's all anyone asking you this would expect.
3. (Original post by Joinedup)
this is an example of a fermi problem / fermi question. googling that term would probably find plenty of examples.

---
I watched a series this summer called 'city in the sky' which had the premise that at any time there are enough people in flight to populate a mid sized city.

so I'd guestimate the population of a mid sized city and divide by the guestimated number of people on a plane.

if you get within an order of magnitude you're doing pretty well - that's all anyone asking you this would expect.
perfect approach, i like this

But if I didn't know the fact that the people flying would populate a mid sized city, how can i approach it?

or they expect me to guess a similar fact? :/
4. (Original post by Daniel Atieh)
perfect approach, i like this

But if I didn't know the fact that the people flying would populate a mid sized city, how can i approach it?

or they expect me to guess a similar fact? :/
Yeah you'd have to guestimate some appropriate numbers

maybe guesstimate average flight time and frequency of landings

this is sort of relevant too
5. (Original post by Joinedup)
Yeah you'd have to guestimate some appropriate numbers

maybe guesstimate average flight time and frequency of landings

this is sort of relevant too
Yes I got what you mean.

I enjoyed the video, and think it's important to know that. Numberphile is awesome.

my last question, if i thought about the problem like how i said in my first post, would it be a bit appropriate? i estimated the number not randomly, and used number of countries. Definitely the ways you mentioned are more logical and better.
6. (Original post by Daniel Atieh)
Yes I got what you mean.

I enjoyed the video, and think it's important to know that. Numberphile is awesome.

my last question, if i thought about the problem like how i said in my first post, would it be a bit appropriate? i estimated the number not randomly, and used number of countries. Definitely the ways you mentioned are more logical and better.
IMO you were on the right lines, treating all countries as being equally responsible for air traffic might be questioned - probably you could have tightened that up a bit.

another useful rule of thumb is the 80 20 rule... it'd be surprising if ~80% of global air traffic wasn't due to the top ~20% of countries.
IMO it'd be easier to estimate the number of landings in the average top 20% country than the average country.
you could estimate
7. (Original post by Joinedup)
IMO you were on the right lines, treating all countries as being equally responsible for air traffic might be questioned - probably you could have tightened that up a bit.

another useful rule of thumb is the 80 20 rule... it'd be surprising if ~80% of global air traffic wasn't due to the top ~20% of countries.
IMO it'd be easier to estimate the number of landings in the average top 20% country than the average country.
you could estimate
thanks a bunch really. was useful

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