Jane Street Rotational Program interview questions

HR replied one day after sending my cv. Written exercise, can be done in any format, mainly aggregation of data and some insights gleaned from the data. Phone interview, scheduled for 20 - 40 minutes but actually a solid hour, one estimation question and one brain teaser. During the estimation problem, the interviewers kept challenging every assumption I made and every number I used. Panic when doing the brain teaser, could not think at all... At the end of the brain teaser, the interviewers asked me how confident I am...I told them around 40%...being way too honest... But have to say the interviewers were really patient throughout the process and gave me guidance when I'm stuck. Did not hear back the next day...guess I didn't pass the phone interview... Now that I think about the brain teaser, it's actually really simple. Stay calm and be clear about your thought process, you will be fine.