The kaplan book was a pretty realistic representation of the QR. The math is not very difficult but it does challenge your ability to quickly reason through a question. Also it is the last section of the OAT so mental acuity and fatigue come into play. The Ada has a practice Oat which also has good questions.
There is a basic calculator on the computer screen during the QR which is very helpful. Also when you do your practice tests be sure to time your self and learn how to skip from question to question so you answer what you know first. Good luck!