I've just recently purchased a copy of the Official GMAT study guide, and am going to start doing the problem solving sample questions. Before I begin - are these in order of increasing difficulty?
Yes. Also, see this post: gmat-study-plan-for-gmat-novices-start-your-gmat-journey-80727.html
Founder of GMAT Club
Just starting out with GMAT? Start here... | Want to know your GMAT Score? Try GMAT Score Estimator
Need GMAT Book Recommendations? Best GMAT Books
Co-author of the GMAT Club tests
Have a blog? Feature it on GMAT Club!