Sample Case Interviews
Practice Case 1: Estimation Case
PROBLEM: How many pieces of luggage do you think are unloaded at LaGuardia Airport each day?
In this type of case, your job is to work through a series of estimations to produce a numerical answer to the question. As the interview proceeds on, you will need to interact with your interviewer, obtain information, and check your thinking. Explain your logic at each stage of the problem, and ask your interviewer whether your assumptions are correct. In all likelihood, your interviewer won't provide you with the hard numbers you need for intermediate steps; instead, the case asks you to make a few assumptions and devise them yourself.
As you work through the problem, think carefully about what assumptions you are making and the ways in which they could be wrong. It doesn't matter if your answer is right, as long as you have thought about it logically and recognized the parts of your solution that you could change to generate the correct answer.
The interview could sound something like this:
Interviewer: Why don't you tell me how many pieces of luggage you think are unloaded at LaGuardia Airport each day.
Candidate: Okay, let me ask a few clarifying questions first. When you say, "unloaded," do you mean baggage that is just handled or that people actually pick up?
I: That people pick up at the baggage claim.
C: Okay. Well, I think we should figure out how many people fly in to LaGuardia each day, and how many bags they carry. A good starting point is probably to determine out how many flights arrive. Now, LaGuardia is mostly a domestic airport, right?
C: Let's assume, then, that there are two kinds of airlines that use the airport. Major carriers that use the airport as a hub will have more flights arriving than those that do not.
I: Sounds fair. So how many major carriers do you think use LaGuardia?
C: Well, let's see. There's Delta, American, United, USAir … why don't we say four major carriers, and ten smaller airlines. Figure that the larger carriers have ten flights arriving per hour, between the hours of 8 A.M. and midnight. Does that sound correct?
I: I think 8 A.M. may be a little early for flights to arrive … that means they would have to leave at around 6 A.M., and there aren't too many of those.
C: Okay, let's say 9 A.M. to midnight. That gives us 150 flights per major carrier per day, times 4 major carriers, which gives us 600 arriving flights per day…
… and so on. The basic strategy, though, is the same for the whole problem. Ultimately, you need three facts:
- the number of flights per day
- the number of passengers per flight
- the number of bags per passenger
Once you have the number of flights, there are several factors to consider when computing the number of passengers per flight:
- Percentage of passengers, by carrier type, for whom New York is the final destination (i.e. passengers who would pick up their luggage at LaGuardia)
- Average capacity per flight
- Average percentage of seats sold per flight
Taking into account both major and minor carriers, you would arrive at an estimate of the number of passengers deplaning at LaGuardia.
The final step is to compute the number of bags per passenger:
- Here it might be useful to distinguish between passengers traveling for business and for pleasure, because business passengers tend to check fewer bags
- Once you have the approximate number of business and personal travelers for each type of carrier, estimate the number of bags you think each type of passenger carries
- Then use your number to calculate the total number of bags passing through LaGuardia each day, based on your earlier estimates and assumptions
The key to estimation cases is in recognizing that each piece of the puzzle must be divided into its parts, and that each part must be analyzed separately.
The conclusion of the estimate interview is supposed to be a number, so keep that in mind as you are driving toward the answer, and be sure to take good notes so that you can add it all up in the end.