A Jane Street Trading Mock Interview with Graham and Andrea

I should throw that out again. 10 or 11 something there where we both don't have much incentive to reroll and try, yeah, so I think the answer should be close to 10, um, okay, so you're saying you're going to play the take money strategy on 10 Ohio 11 Ohio just uh yeah it doesn't matter but give me something to be concrete yeah right 10. 10 or more okay so what do you think the casino is going to do? Well, if he sees that he still sees a 15 or something like that, he'll roll again for me too. Okay, and put me down for next time.

I guess if I roll a 10, the casino can let me keep it because a 10 is less than the expected value of their next roll. So why don't we imagine ourselves playing this? Go out and see what it would be like, see how much money you will win so to be specific you are playing the strategy of taking money when it is 10 or more and the casino is playing the strategy of rerolling elevens Ohio uh. yeah ok so let's see how much money we can see or win in this game sorry can the casino make this game sorry how much money will you win in this game oh um if people played these strategies , oh, I got you, eh, let's see. so if I roll a, let's say there's about half a chance, uh yeah, it might be easier to think of, let's say, a casino and we both have the same strategy of 11 or more, so like we do some, we do our movement so that you and they both agree that 11 and up are good for you and then you want them and they want to roll them back, okay, sure, yeah, yeah, so this seems like a swing between, for example, if I roll a 10 or less half the time, then the casino will just let me not want to reroll for me, huh, versus if I get 11 or higher, the casino will immediately reroll the next one, sorry, just to clarify, the casino only has the option to reroll once you take the money. not only can they reroll every turn uh oh hey yeah I got you yeah um so if I say 11 or more and I decide to keep it then the casino will reroll me okay so in that case yeah, so let's go.

Let's say the situation ends with me winning like 15.5 and then Casino will start working, so after that I have to start from scratch, so every two roles I meet my criteria of 11 or more so then I can play like 50 times this sequence of events , uh, and I get like 155 of them, so I guess I expect to get like 775 bucks playing this strategy, okay, yeah, that sounds pretty good, okay, so how much money are you making per spin, in that case? I'm making like seven eight dollars, so yeah, in that case maybe that means I should change my thresholds.

Oh, what do you want to do with that? Let's see, okay. So if yeah, if that's seven eight per roll, then if I get an eight, I should. Don't think badly and maybe just take the money. Yes, it is very possible. Yes. Why don't we calculate how it goes and see if it is better. Yes, that seems reasonable. Okay, so if I go from eight to twenty, then like 14 on average. I can play this up to 13 20 of the time, so, sorry, remind me to take the money, that's a move. Yeah, okay, I got you, so I would expect 20 over 13 plus one, so 33 over 13 is like the number. of how long a sequence is, I think maybe you don't want that plus one, okay, because you can see the casino starting role for free, like the casino gives you something random, yeah, okay, give me that one, Alright.

Sounds good, cool, so a hundred more than that, so I get 13 out of 5. uh, which is um 2.6 uh, wait, what did I just do? uh wait, sorry, so there's a hundred rounds and then I have 100 rolls like before and then each sequence. it takes me 20 out of 13 times, so okay, yeah, then I have to play this 65 times great and then 14 each time, okay, so that's 130 times 7 and then I play it, yeah, 910, that's more than before, yeah, great, okay, uh in that case I should increment by uh yeah, I think I was already right about this, but yeah, um, yeah, the answer is probably somewhere between the two, yeah, yeah, okay. , that's really good, I think we'll stop the

interview

here, of course, in a real way.

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, there could be more questions or I would stop at the end and ask Andrea if she has any questions for me about Jane Street or the internship you might be applying for or anything else, but for now it's okay, thank you very much.

Thank you so much for your time, thank you for the benefit of people watching this video, let's talk about how we thought it went, first of all Andrea. I think you did very well on that question. Thanks Graham. I'm still getting upset about some things but Overall I agree, I think it went pretty well and to be fair you are already a trader here so I hope you do well not just because you're smart obviously but also because of the experience he has working on problems like this. So if you're watching this video and feel like you wouldn't necessarily have been able to go as far as Andrew did or progress quickly, don't be discouraged by that.

Anyway, initially it took us a minute or two to really get on the same page about the question she was asking, that's totally fine, it can take a while to understand a new problem and it was really good that Andrea kept clarifying until she understood what I was asking, yeah, I wasn't really sure. how much to push there, but I thought it would have been very sad if she had worked hard on a question that turned out to be the wrong question. Yes, that would have been unfortunate. I think it was pretty good to keep clarifying and that leads. to communication in general I thought you did a great job of explaining your thought process to me, sometimes that just convinced me that you knew what you were talking about and other times it helped me know when to clue you in or correct a misconception.

I recognize that it can be difficult to think and speak at the same time and we don't really expect candidates to talk as much as you, but I think you demonstrated why we find it important to think out loud. Yes, this is something I remember getting some advice from my interviewers when I was going through the process myself, they encouraged me to think out loud and it was very helpful, of course, it feels much more natural now that I've been working here for a while. time. A lot of my day is spent thinking out loud, but I remember having to be quite aware of it when I was interviewing and the quantitative aspects of the question.

I thought you did a good job of thinking through the problem and breaking it down into smaller, more solvable parts. pieces I liked how sometimes you would work on a strategy to see what happened or if that would generate better ideas to work on, even if it wasn't necessarily going to be the best strategy overall, we found these to be useful problem-solving techniques and Overall, this iterative and collaborative problem-solving process best replicates what it would be like to have a conversation on an operating table here at Jane Street and when I gave you clues, you were able to really take them and run with them, yes, there are a lot of them.

I really appreciate it, thanks Graham, it was a lot of fun working on it, it reminds me of my own Gene Street interviews in the past which were also a lot of fun, to be honest I was quite nervous before them, they were some of the first interviews I had. I've done it a few times, but my interviewers really put me at ease and made the process seem more like an exciting discussion than an interview. Excellent, we hope you enjoyed this video and good luck with your interviews.