Regardless of the source of questions the Reed's books will provide you with most of the information required to answer the questions.
I would suggest tackling the questions in the book first to refresh you math skills, and then practice answering questions from other sources where the answers are not so readily available to hone your ability to calculate a solution.
Remember the whole purpose of the exam is not an exercise in math, but to prove your ability to do calculations necessary by using the correct formulas and steps, to help solve problems in the real world with the raw information made available to you and the answer is both accurate and correct.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"