Meta Data Scientist, Analytics PhD interview questions

There are three rounds of the interview. For the first round, you will have an interview with an HR person (~15-20 minutes). The second one with the data scientist at Facebook. It took around 45 minutes - an hour. I did not pass this round, so I don't know how the third round would be like. Also, I like that Facebook provides the materials for interviewees to study before the actual interview.