The process took 1 day. I interviewed at Group One Trading (Philadelphia, PA) in Feb 2010
Interview
Applied online through a posting on the company's website for a summer internship. They had a phone interview that started off with qualitative questions about why I wanted to be a trader, why I applied to Group One, etc... Then there were some simple mental math and probability questions. The key for these questions was to be able to explain the process you were going through as you were making the calculations in your head.
Interview questions [1]
Question 1
How many degrees separate the hands on an analog clock at 3:15?
I applied through other source. The process took 2 weeks. I interviewed at Group One Trading in Feb 2012
Interview
Phone interview went well, quick mental math questions and some behavioral questions. In office interview did not go well. Pretty clear from the get go that the interview and me were not the same type of person.