Hey there,
The McK interviewers mindset is to collect enough valid data points on your performance to make a clear statement on your success or failure. If you excel 3 case questions, the case might end and you move on to the next round.
On the other hand, if a candidate is able to go through 6 questions in 25 minutes that could indicate that
- the structures are not creative or exhaustive
- insights were missed in the charts and implications not properly discussed
- math was faulty
GeneraIly, if your performance is stellar in some questions and lagging in others, the interviewer has more ‘’backup'' questions to ask and test more specifically (''was this just an outlier or is he really struggling with math?'').
In the McKinsey interview you should take your time to ensure a stellar performance, rather than moving quickly through the case, and that most of the time means you won't go through all questions of the case.
Quality over quantity!
I have written a detailed article to shine more light on this here: https://www.preplounge.com/en/mckinsey-interview
Cheers,
Florian