One of the most important feedbacks I give to the candidate - don't ask multiple unrelated questions at once. The interviewer will not remember all of your questions and you will have a wrong impression that you have asked all of them=)
re your 3,4 questions - you can expect any kinds of cases, so you should be prepared for anything. regarding the jokes - be careful here. Not all partners will accept them. You should behave professionally!
As for the 1st question - it comes with practice.
First of all - not all issue trees can and should be MECE. Very often it's not the case.
Secondly - there is a number of ways how you can approach in a MECE way:
- If your structure works mathematically (e.g. Total time spent on cleaning operation = # of people x Frequency x Hours per cleaning per person)
- If your structure comes from a formula (e.g. output rate = total number of people being served / time to serve one person)
- If you are using the common industry drivers (e.g. revenues = # of customers x av. check) (e.g Passengers on the plane = capacity x Load Factor) or theindustry revenue streams (Fuel revenues / non-fuel revenues for the gas station) or the functional drivers (e.g. for the problems in sales : Sales strategy / sales people and allocation / motivation / sales process)
- If your issue tree is a real framework used by the consultants (e.g. the famous Bain Cap framework for PE due dills: Market / Competitors / Company / Feasibility of exit) (e.g. People / Process / Technology) (e.g. The famous McKinsey framework - People don't want to do smth / they can't do smth / smth prevents them from doing that)
- If your structure is a well-known academically MECE framework (e.g. Product / Distribution / Price / Marketing (Also known as 4P))
There is no magic pill how you can learn to build the MECE issue trees. !!!! It comes with a lot of Practice and reflection and building proper industry and functional knowledge. !!!!