2 combinatorial problems:
1. Coin toss problem requiring a Markov chain application. Needed to choose the optimal strategy in the game.
2. 3 bags and colored balls problem, asking the EV of number of balls to be drawn.
Interview questions [1]
Question 1
Q: What is the winning strategy in the game where you toss a coin aiming to get some sequence?
1st round--45 minute phone call purely technical with brainteasers. no behavorial besides brief introduction of self. i believe there are 2nd and 3rd round phone and a final superday but didn't make it past there.
multiple online interviews, technical in nature, followed by an in person in office interview which lasted an entire day and had multiple stations. focused on problem solving, probablity, game theory etc etc
I applied online. The process took 1 week. I interviewed at Jane Street (London, England) in Nov 2025
Interview
They started with a basic introductory question followed by some probability based stuff. Wasn’t too difficult but you have to ace it, they expect perfection. They cut the interview off at exactly 30 minutes, and will provide hints if you need it though it’s not a good sign if you need them.
Interview questions [1]
Question 1
You have 20 cards. 1 is black the rest are red. You keep drawing cards and get $1 for each red, but if you draw the black the game ends and you get nothing. How do you play and what’s the average payout? Now drawing the black card makes your score go negative, but you can continue drawing cards. What’s the strategy and expected payout now?