how many pieces of luggage are unloaded at Boston airport on an average day?

harvardgrad08

I would approach it as follows:

1. First step is to clarify...does the interviewer want to include only bags being unloaded (arrivals) or do they also want bags being loaded (departures), do they want to include carry on bags or not. They will usually have an answer for you here. For this example, lets assume they just want total bags unloaded from planes and don't want you to include carry on bags.
2. To start lets make an assumption as to the number of gates there are at Logan -- here we'll say that because it's a relatively large airport it has 100 gates. (remember to always use easy whole numbers)
3. Make an assumption as to flight operating times -- we'll say that flights generally operate between 6am and 12pm meaning there are 18 working hours
4. Make an assumption as to how frequently a flight arrives at a gate -- let's assume it's every 4 hours as you are likely to have few very early and very late arrivals plus hold times for departures, etc. so it'll average out at 4.
5. Given the above this would mean that there are ~4.5 planes (18 hrs / 4 hrs) that arrive at each gate daily for a total of ~450 arrivals.
6. Next make an assumption as to average number of people per flight -- for this we'll assume that most planes have ~30 rows with 6 people per row so on average a capacity of 180 people...we'll assume most flights are 75% full so 135 passengers are on each flight on average.
7. Next make an assumption as to the number of passengers that check bags -- we'll say that b/c of recent baggage fee policies implemented by airlines only 1/3 of people check a bag so we'll say 45 people per flight.
8. Make an assumption as to the number of bags per passenger -- we'll assume it's only 1 bag / person.
9. Note that even passengers that are in-transit (e.g. layovers) generally need to have their bags unloaded and reloaded onto another plane so you will include these bags in your unloaded number meaning that all bags arriving in Boston are being unloaded (even if they have to be re-loaded later).
10. Solve for the total number of bags -- 45 people per flight x 1 bag / person x 450 flights = 20,250 bags per day are unloaded at Logan

Note: obviously you can make it more complicated if you want by adding variations in the sizes of planes arriving (x% are small planes, x% 747s, etc.), adding number of bags being shipped on cargo planes, etc. but i generally try to keep it pretty simple...

**if you actually look at Logan's real numbers these guesses are actually not far off...they have 103 gates and ~972 daily inbound and outbound flights --- so our 450 number for arrivals is not bad actually.**