This book is full of typos and mathematical errors. It really serves to deligitimize Project Management as there was clearly very little quality control or assurance put into this project. I'm currently trying to get my money back. I've found many questions to be inconsistent with the current version of the PMBoK, that this book is supposed to reference. The CD with mock questions on it is an absolute joke. The question explanations are just a rephrasing of the question, with no expanding information. Choose another book or study aide. This one will not help you.