Out of the blue I got a call from a recruiter saying that bank X would like to interview me for a quant role they have. They wanted to fast-track the process so they booked me for 2.5-3 hours of back-to-back interviews. I was not looking for a new job but I thought it might be good to talk to them and explore leaving academia.
The first interview was with some quants who work for the hiring manager. They tell me that they plan to have a technical talk with me and then follow that with some math problems and brainteasers. At that point I respectfully declined saying "I wasn't aware that I was going to be asked those types of questions and I don't really believe they are a good hiring tool". The guy tells me too bad, that's the way they hire now. I say fine and we carry on with the first part of this session and have a technical talk.
We then come to the point that they want to ask me the math problems. I again say that it's silly. They disagree. Then I say "For example, who's to say you're not going to ask me problem A". They laugh. "followed by problem B, C, D". They stop laughing. "Finishing with the problem about the expected number of tosses of a coin to HH". They look at each other. "and who's to say that I don't know the answers by heart. It's luck of the draw, maybe I know your questions and maybe I don't and how would it reflect on me if I don't know". The guy who had problems ready for me turned white. They quickly ended the interview in a cordial way at that point and seemed to scramble to find the next two guys to come and interview me. Probably because the interview finished 30 mins earlier.
What they didn't realize is that I love these types of problems and that it is a small community. I know a lot of people and remembered what questions they had asked one of my friends. When they walked in the room, the guy had the solutions written out on a piece of paper and with only a brief glance I knew that I was going to get asked the same ones.
He had paper with the solutions face down during the whole interview but when he left I have never seen anyone pickup a piece of paper in a more awkward way. He did the whole fold in half as you lift thing.