The Ultimate GMAT Quant Guide Part One is now available on ibooks for iPad priced at £12.99 (which translates to $20):

UGQG1 on itunes

If you download the free ibooks app you can view a sample (most of Chapter One).

If you then go on to buy Part One, I’d be happy to forward you groups of question numbers for the medium and difficult Problem Solving questions by topic, together with my explanations as required. I also have explanations to most of the Data Sufficiency questions (the ones that were in the 12th edition of the OG).

I’m not a big fan of Apple but their ibooks author software, intended primarily for textbooks, is new and very nice. I hope my book and others like it will be available for Mac, and then PC, in the near future, but as usual with these things that depends on Apple.