Can anybody suggest few good books on quant? I have come across some books but those problems are too simple.

In CAT generally problems are little complicated. So I am not really getting any good book. Can anyone suggest any book where there are some tougher problems. But keep in mind I am looking for some books where problems are reasonable. CAT questions are never too tough. But they end up taking a little more time then what they should. So I am looking for some books like that. Please help....