Jane Street
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www.janestreet.com New York, NY 150 to 499 Employees

Jane Street Assistant Trader Interview Questions & Reviews

Updated Jul 1, 2014
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Assistant Trader Interview

Assistant Trader

Interviewed at Jane Street

Interview Details – It was a similar process to what others have already described. You have to be ready for the types of questions they will be asking, otherwise you should probably wait on that interview. It's not very hard to get the initial interview, but keep in mind that you'll go through progressively harder interviews.

Interview Question – Similar to what others have stated, make sure you know basic probability, combinatorics, and can do these in your head.   Answer Question

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Assistant Trader Interview

Assistant Trader
Princeton, NJ

I applied through college or university and the process took a day - interviewed at Jane Street in February 2014.

Interview Details – Basically, they want to know how much math you're able to do, quickly and efficiently. Knowledge of expected value is a must, as is basic computational skills. You don't necessarily need to be able to think outside of the box, but they're going to want to see exceptional problem solving ability.

Interview Question – You are given a die with 100 sides. One side has 1 dot, one has 2 dots and so on up until 100. You are given a chance to roll the die and, however many dots come up, you can choose to (a): take that many dollars, or (b): pay $1 and roll again. You can continue to reroll as many times as you see fit, but you only keep the money of the one roll that you choose to end with. What is the optimal strategy and expected value?   View Answer

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Assistant Trader Interview

Assistant Trader

I applied online and the process took 2 weeks - interviewed at Jane Street.

Interview Details – telephone interviews just brain teasers. Missed a trick on the first interview but they still wanted to schedule a second one so it's mostly about the reasoning.

Interview Question – person A has a 30 sided and person B has a 20 sided die. both players role and the person with the highest role win (on a draw B wins). the loser pays the winner the value of the winners die.
1. calculate expected value of this game for player A (easy)
2. how does this value change if player B can re-roll and when should he re-roll.
3. now how much is it worth for player A to get a re-roll option in this scenario.
4. remove player A reroll. how many re-rolls do player B need in order for him to be a favorite in the game.

i believed i solved 4 and 2 I had a decent idea but 3 is very difficult since optimal strategy might change based on opposing players optimal strategy.
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Assistant Trader Interview

Assistant Trader

Interviewed at Jane Street

Interview Details – They were pretty slow in their follow up after interviews, I had to email them every time before they'd remember to send me to the next round. The interviews were interesting and technical. Be prepared to answer questions quickly, without pen and paper, in the first round at least. Later on the questions get harder but they allow you to use writing materials.

Interview Question – I did initially misunderstand this question and had to be helped along, but it is fairly difficult to do on the fly anyway: "We're playing a game with an unbiased 30-sided die. Before we roll, we both pick (distinct) numbers between 1 and 30, and then we roll the die. If the number that appears is closer to the number I picked, you pay me, in dollars, the number on the die; if it is closer to the number you picked, I pay you, in dollars, the number on the die; if it is equidistant we do nothing. What's the optimal strategy - do you go first or second, and how do you pick your number? What's your expectation?"   View Answers (2)

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Easy Interview

Assistant Trader Interview

Assistant Trader

I applied through college or university and the process took 2 weeks - interviewed at Jane Street in February 2014.

Interview Details – Applied through university. Got an on campus interview. Very laid back, just a few basic multiplication questions and probability questions

Interview Question – You have a dart board thats split in half. If you hit the left half, you get 2 points, if you hit the right half, you get 3 points. If you have an 80% chance of hitting the dart board on any given throw and a 70% chance of hitting the side you're aiming for (given that you hit the dartboard so a 30% chance you hit the side you aren't aiming for), if you have an unlimited number of throws, what's the probability you get a score of exactly 7   View Answers (4)

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Average Interview

Assistant Trader Interview

Assistant Trader

I applied through college or university and interviewed at Jane Street.

Interview Details – On campus review

Interview Question – If you could ask one true or false question to all Americans and wanted to minimize the number of people who got it right, what would you ask?   View Answers (2)

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Assistant Trader Interview

Assistant Trader

I applied through college or university - interviewed at Jane Street in February 2014.

Interview Details – Used the university campus recruiting website to apply. I was notified a week later that I had gotten a first round interview. The first round interview had no fit questions - only mental math questions and probability questions. I was notified the day after that I got a second round interview, which would be the following day. The second round interview was significantly more difficult than the first. No mental math questions - just a questions about different games asking what the expected value of the game was and how I would bet on it.

Interview Question – Two dice - one 10 sided one 6 sided. Guess the roll of the two dice, no penalty for guessing under. You receive the amount on the dice if you guess it.
What is the expected value? What is the bet that would maximize your payout?
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Assistant Trader Interview

Assistant Trader

I applied through college or university and the process took 1 week - interviewed at Jane Street in January 2014.

Interview Details – I applied through my school's online recruiting system. I did an interview with a man who seemed friendly. I didn't think I had done too well but I got the email for the second round, so apparently I did well enough (I haven't done the second round yet). I'd advise just really showing your thought process, since they care about that more than your actual answers.

Interview Question – Given a black box that spits out random numbers from 0 through 1 (probability distribution can be random) such that events are independent and the probability of drawing any one number is 0, simulate a coin flip (with EXACTLY 50% heads, 50% tails).   View Answers (3)

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Assistant Trader Interview

Assistant Trader

I applied through college or university and the process took 2 weeks - interviewed at Jane Street.

Interview Details – Seemed like really nice people, the interview questions honestly were just basic probability and mathematics. Just don't freak out and they shouldn't be too much of an issue.

Interview Question – Asked 4 mental math questions, then asked a bunch of probabilities about them (such as, chance i got them all right, chance i got the hardest one wrong, chance i got the hardest one right but a different one wrong etc).   Answer Question

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Assistant Trader Interview

Assistant Trader

Interviewed at Jane Street

Interview Details – Applied through on-campus career center. I had an interview scheduled about a month later.

Interview Question – Many stat questions. I didn't even get to the hard ones.   Answer Question

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