How many planes are in the sky right now? (Interview question)
How would you go about structuring your approach for this question?
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Many ways to think about it.. here’s one..
About 200 countries in the world
On one end, we have countries like US which has let’s say 250 airports. On other hand we have countries such as Madagascar which has may be 1 airport.. so let’s say an av of 10 airports per country ..
200x10=2,000 airports worldwide
In the US, in LA for ex planes take off every 5 mts or so… in India it’s more like 20 mts or so… most airports worldwide operate 18 hrs a day (6 hrs for op maint work) let’s say on average a flight takes off every 30 mts for 18 hrs a day - so 36 flights taking off(and land)
2,000 x 36 = 72,000 flights taking off, on equilibrium, the same should be landing(hopefully!)
what’s the average flight time? Let’s say 3 hrs? (Anything less than that most people take a car or train!) 72/3 = 24k commercial flights in the air around the world ..
sounds reasonable I think
Update: per below, 72k flights in a 24 hr schedule. If we assume a 3 hr flight time, 24/3=8 cycles per day, so as someone pointed out 72/8= 9k flights in the air (good catch! And thank you…)
This is 100% the correct way to approach this, but for OP - just to make the point... the answer literally doesn't matter, you just need to learn how to think through explaining something to someone instead of "how TF would I know that?!" or worrying your number is way off.
This is a great interview answer and the actual number is 7-8k planes at any given time, but you could arrive at 50k with the above logic and as long as you walk your way through it that's what they want to see. Don't get too caught up in estimating numbers or actual truths, just use very round numbers and explain how you get there.
Right, but the math in the last step is wrong, you shouldn’t be dividing 72k by 3 hrs, the avg flight time should be directly proportional, so it should actually be 72k/(24/3)=9k
Other reply seems to indicate our assumptions are quite good here as well
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