The following corresponds to the green cover book - ”The Official Guide for GMAT Quantitative Review – 2nd Edition.” (Google Books Preview – opens in new window) Unfortunately, there are not that many difficult questions. I would say the questions are mostly 650 level and below.
Problem Solving Questions (OG Quant Review Second Edition)
Data Sufficiency Questions (OG Quant Review Second Edition)
Data Sufficiency Questions (OG 12 Edition pp. 273-288)
Some OG 12th Questions are linked to Khan Academy.
You might be wondering where the whole question is. For copyright reasons, the whole question is not shown. A few words are shown to help you keep track.
For comments, suggestions, errors, or anything else: email firstname.lastname@example.org Enjoy!