Applied for assistant trader intern. There are 5 rounds of interviews; first four are phone interviews and the last one is an on-site interview. I only made it to the fourth round and didn't break into the last one. All are mental math, probability, problem solving, with increased difficulty. as you go further in the process. Problems are really challenging, and you need to be able to explain how you get the answers. The traders I talked to are easy going and friendly, and they sometimes give hints to guide you to the right answer.