Upstart Data Scientist Interview Experience — One Tech Screen, a Two-Round Virtual Onsite, and an Offer a Week Later

Overall the experience was quite good — the HR person and the several interviewers I dealt with were all very supportive, and none of them looked down on international candidates. There was no HR screen; I went straight into the first technical round. The interviewer didn't ask about my resume at all at first — just had me do a quick self-introduction and then went straight into questions. The questions were:

1. Atom half-life is 1 day. What's the probability that, out of 100 atoms, some number are still alive after 10 days? Write a simulation — input: number of days m, number of atoms n, output: the state of the particles.
2. A classic Bayes' formula question, very simple — you just plug the given conditions into the formula.
3. Implement a factorial function in Python, then explain how many ways there are to compute the number of trailing zeros.

Less than a week after that, HR called me directly and said I'd made it to the final round, that the invitation was still being processed, and that they'd send me the scheduling link in a few days. In reality it took more than a week after that call before I actually got the schedule, and at one point I thought I'd been ghosted. The final round was two back-to-back virtual onsite interviews — one on probability & stats, one on stats & ML. One of them had a 30-minute resume portion, and the other one just went straight into questions. The questions were:

1. y = x + e, where x and e ~ N(0,1) and are independent. Do OLS regression of y on x and of x on y, and give the coefficients.
2. The classic Monty Hall problem.
3. An n-sided fair die — what's the expected number of rolls needed to see every face at least once?
4. The difference between L1 and L2, and the difference between ridge and lasso.

It's kind of funny — I think the interviewers hadn't coordinated with each other, because two of the questions were actually repeats from the first round. I suspect they have a question bank and each interviewer just pulls from it. Honestly, compared to a quant interview, these questions were really easy. The day after the final round I got an HR call saying I'd passed, and a week later I got the offer. The whole process was communicated pretty smoothly throughout.