It's long and tough, but the interviewers are keen to see you do well and give tips here and there. They also give great feedback on how you went.
Generally problem solving questions, with numerical skills also being tested.
Brush up on mental arithmetic, be able to explain what you're thinking when solving problems, that way the interviewer can see what you're doing, as they'll help you out a bit if they think you're going down the wrong direction.