I was doing a mental calculation (something simple like 210 * 700) and left off a zero when I said the answer.

Just drying up completely. It only happened once thank goodness. From the looks on their faces, the interviewers seemed to be finding it even more painful than I did. If I ever felt that situation happening again, I would slow my breathing - as when you do that the whole body relaxes and you can think clearly again. Tip: on the pause between the out breath and the in breath it's impossible to think of something unpleasant, so just for a moment go into that space and "reset" yourself.

(First post). First round interview with an industry coverage team at a London bulge bracket - I was left completely stumped by a (relatively) simple brain teaser. The question was as follows: "You are at a networking event with 500 other investors. What is the probability of you sharing a birthday with a minimum of one other attendee?". Needless to say I spent about five minutes talking aloud to arrive at the answer (hint, it's 100%).

Yeah that's an easy one. Probability of meeting with someone who shares your birthday is 1/365. Given its 500 people at the event it's definitely going to happen. Am I correct?

Maybe easy for you! That's correct - once the sample size is above 365 (365.25 including leap years?), the probability approaches 100%.