I have an upcoming interview with BCG and am struggling most with math. I am good with writing down math and doing it but my problem is that I do not really use any shortcuts and tend to make mistakes if I am not writing everything down and doing it step-by-step. This makes it so that I take a while to do math and I feel somewhat like a primary school kid when I am writing down everything (carrying a 1/long division etc). Is it better to just do the math this way and get it right or should I take the risk of trying to do math in my head or ways that I am not used to just to go a little faster? Overall, just want to know if speed or accuracy should be compromised if I cannot deliver both which would be ideal.

In addition, also curious how much of the math I need to actually say out loud. For example, I might say, I am going to divide X by Y to get Z. Can I then be silent for a bit when I do the actual operations?

Thank you for your answers!