Many interviews now concentrate on giving people technical and mathematical quizzes. You can get books to help prepare for them.
Quizzes are good at finding out how fast someone can think on his feet, or how rapidly someone can solve a PDE, or how good a programmer he or she is. All of this is useful knowledge if that’s what you’re looking to hire.
But quizzes aren’t the best way to find out what someone is capable of in the long run. (Call me old-fashioned but) I always liked to ask interviewees what they had worked on or studied before they came to me, and and to explain it — it’s relevance, how and why they went about it, the result, how to understand it. I didn’t want to see if they knew what I already knew — I wanted to see how well they knew what they said they knew, and how well they could explain it.