Three rounds of phone interviews, in which I was asked math questions of increasing difficulty. There was a large focus on probability and combinatorics, which most of the problems phrased as trying to determine the optimal strategy for a game; however, as I indicated that I come from a CS background I was also asked to design an algorithm to solve a problem with a good asymptotic runtime. The first and second round should be relatively easy for anyone that majored in a quantitative subject, especially math, physics, or computer science; the third was vastly harder- I was unable to answer the problem correctly without significant guidance, but passed this round nonetheless (presumably, they really do care about the nature of your thought process).