Regarding estimation questions, my friend recently did a first round interview at Booz and Co and the first interview, the full hour was dedicated to estimation question. I was wondering if i should expect that at a Mckinsey interview, or do they usually appear as part of a business case?
It's unusual to get a one-hour estimation question. McKinsey first rounds in most part of the world tend to be interviewer-led cases. So they give you some basic case information, and then they ask you questions about the case.
In situations where this is not the format, you're more likely to see either a few estimation questions or a business case where it is candidate-led with an estimation question sometimes included within the business case.
For the more open-ended format, keep in mind each individual interviewer has remarkable leeway in terms of what they ask. Most candidates think it's some big coordinated effort.
Sometimes it's just the recruiter roaming the hallways inside McKinsey says, "Hey, my interviewer called in sick, are you free to do a few first round interviews for me?"
This is how I first started interviewing.
Do you know how much time and thought I put into the question I would ask my candidates? About 60 seconds. The time it took to get from my office, take the elevator down three floors, and to meet my first candidate in about three minutes.
I made up the case during the elevator ride.
Every individual interviewer is different and they in large part pick whatever case they want to do. Some will coordinate with others (you wouldn't want a final round to be six hours of only estimation questions) and some will certainly coordinate who will do a case vs. who will do a consulting resume-type interview.
But once an interviewer is designated to do a case, they will in many cases use personal preference to pick the case.
Also, some will not intentionally plan to give an estimation question in the middle of a business case. But sometimes, a candidate is solving a particular part of a business case and a quick estimation question is just a natural next step -- so they'll ask it right then and there.
By the way, this happens on the job all the time. A client asks you some unexpected question. You don't have access to the company's computer systems, so you do a quick estimate to see if the client's idea is remotely feasible.