I have been preparing for an upcoming McKinsey interview as BA. I read up on the theory books as well as all of PrepLounge's BootCamp articles and have already done 25 case practices with a partner. As my qualitative part and structure improve, I noticed that one struggle I never seem to overcome is the quantitative part. I have no problem with the calculation itself but I struggle to find the most efficient way to the solution when presented with a problem and therefore take up more time to solve a case because of quant. This is despite the fact that I have already reviewed all the quant concepts from PrepLounge and other sources. How can I improve this besides just doing more and more cases?
Additionally, what is the expected level of quant skills for McKinsey interviews? The sample cases on their website seem quite doable but in some case books I've encountered, the "McKinsey" cases had really elaborate calculations, so I'm not sure which one is closer to reality.