Hi there,
Firstly, HUGE CONGRATS on making it through the McKinsey interviews - that's no easy feat!
The fact that HR is scheduling an interview does not necessarily mean that you passed the 3rd round. Most likely, HR just wants to give you an opportunity to ask any final questions you may have regarding the job, the office, their approach to staffing, and to hear about your preferences.
This could also mean that during the interviews, an idea came up that you may be a great fit for a different role (e.g., Expert track or specific Industry affiliation), and they may want to check if that's something you might be interested in.
Obviously there may be other reasons for the meeting, but I'd bet it's nothing negative :)
Hope this helps, and crossing my fingers that you land the job!!!
Sincerely,
Thor
Also from your experience, is there a chance that if I made math mistakes I could pass? Or is it something very negative?
Yes, you can definitely pass even if you made a math mistake. That is only one part of the full evaluation, and if for example you did quite well on that part in other interviews, they are likely to just chop it up to nerves.
Sincerely,
Thor