Well as book title says it is official guide and it has more than 800 retired real GMAT questions, its good book to start your GMAT preparation.
Number of Question in each sections are
Problem Solving : 230
Data Sufficiency : 174
Reading Comprehension : 139
Critical Reasoning : 124
Sentence Correction : 140
And there is one Diagnostic Test as well so 100 more questions.
Please Note if you already have The Official Guide for GMAT Review 11 then there are only 200 questions are different in this editions.
Following points about this book.
1. This gives you real taste of real GMAT questions.
2. But this book is not for building your basics or concepts for that you should buy some other book such as
Manhattan GMAT, Set of 8 Strategy Guides.
3. Along with this book try OG verbal and OG quantitative.
4. Problem in this book comes with clear explanation why one choice is right and why others are wrong.
I find the paper quality of this book is not very good paper are very thin.
Overall if you are serious about GMAT this is best place to start, and you need lots of practice.