Hi, so I just concluded my McKinsey final round interview (1 of 2) - the interview was structured normally, a PEI section followed by a case interview. I felt I performed well on the PEI and was able to answer all questions the interviewer had about my experience in a structured manner.
The case itself was a public sector case, greenhouse gas emmissions for a country, particularly focusing on the power generation industry. My overall approach was highly customized, well structured and properly communicated (numbererd buckets, clearly speaking, and making relevant statements with regard to the country in question) - the interviewer said she was satisfied with the structure.
Following this, I got an exhibit with a number of data points, here I was quickly able to share level one insights in a structured way as well as calculate level two insights and share those as well. In addition, I connected back to my orignal hypothesis and structure confirming certain parts of it for a deeper analysis.
Here comes the problem, following this I had to do what I would call a simple math calculation - calculate the percentage change in emmissions in the previous period, double that, and apply it to the current period to see what the end result would be of the proposed strategy (told in the prompt) - I laid out my approach, broke it down into steps and confirmed the approach with the interviewer (in laying out and confirming I explicitly said I would double). I talked through all the math and did it correctly BUT missed out on the doubling of the percentage change.
This ofcourse threw off my final answer.
My follow up 'so what' was good in response to my calculation (which was off of course) but here's the thing, the interviewer DID NOT point out the concern or anything. All she said was wonderful thank you and we moved on in the interview to the closing conversation.
An important point to note, the final conclusion was correct just off in the gap i.e. country was NOT meeting target but by how much I had calculated wrong so, my follow up 'so what' was correct as well as the final reccomendation.
Overall the interview vibe was good, smiles on both sides and good communication overall so I want to understand:
a. Why did she not hint towards the error b. How badly am I screwed here
Please do let me know, thanks.