For those who need a thorough preparation in GMAT Data Sufficiency, we are proud to recommend our new app, created in collaboration with Simply Brilliant's Stuart Park, who is simply the world's best GMAT tutor.

Download the free app: http://itunes.apple.com/us/app/gmat-prep/id541985313

Stuart's profile: http://www.simplybrilliantprep.com/Credentials.html