Hi,
i purchased the OG 11th edition a couple of weeks back. i noticed that the front cover says "answers to 800 real gmat questions". a friend of mine gave me the OG 10th ed yesterday. my eyes lit up when i saw "answers to 1400 real gmat questions". so does that mean 600 extra questions in the previous edition, which was the primary driver for my excitement. how much of a content overlap in terms of a percentage figure would i find between the two as i get down and solve these questions?
thanks

The latest publishing round was split into three books: OG11, a quant supplement and a verbal supplement. OG11 has 800 questions, the Quant Supplement has 300 questions, and the verbal supplement has 300 questions... for a total of 1400 questions (which matches OG10). There's about 75% overlap in the full set of 1400 questions.

So, if you only have OG11, then many of those questions do appear in OG10, but the rest are new for you (again, as long as you don't also have the two supplemental books).

i have the GMAT OG 10th edition and 11th edition with me. does that mean i dont have to purchase the GMAT OG verbal guide?
thanks

About 75% of the questions in the verbal guide appear in OG10. Up to you whether you want to purchase the verbal guide for the subset of new questions!