The interviews are split into 2 different levels, first being mini case and later being the power day one. I had prepared for the mini case through the Hacking the Case Interview book and general glassdoor interview reviews. Also do go through their youtube videos for a sample mini case experience. I would emphasize having math calculations up your sleeve and being quick with that. As the glassdoor reviews had said, the case interviews will usually involve break-even analysis. In my particular interview experience, I was pretty nervous as it was my first mini case interview but overall a learning experience. Moreover, they follow a script and not really talk with you about the case. I however, made a few basic math mistakes and I knew that this interview was not going to go well. My case had a lot of data and in especially confusing terms including hours, half-hours, months and years. The interviewer also steered me in the right direction with related to the data and calculation. Another tip I'd like to share is that don't be nervous and talk to the interviewer about your process of calculations.