@kvcpk: Thanks for your interest in the matter and your initiative in looking into proper references.
There are many GMAT problems where the word
positive is wrongly missed, therefore the official answer is wrong but we have the "luck" of choosing between NUMERICAL answers only (and none of them is really the right one), and then we realize their mistake and still have the opportunity to click the answer the "think" is the right one. I tell my students: "you know they are wrong, so what? Make them happy!"....
In this matter, if you have the "None above" alternative choice, I know it´s hard to decide, but I guess the best advice is: put the RIGHT answer, because some EXCELLENT students will put the "None above" as their choice and (we hope) the GMAT will verify that (Statistically speaking, by cluster analysis for instance, this is not hard to detect...) and they will probably correct the "answer sheet" "afterwards"... yes, this is the idealistic scenario but, hey, it´s better to do it right and believe they will detect it... right?!
@goyalsau: "Because if we consider formula that we use for years for factorizing will prove wrong"
No Sir, please do not forget that the formula you use for years is for calculating the number of POSITIVE factors of a given integer, therefore this formula should have a 2 TIMES it if you want to consider it for the "general scenario".
In this matter, the fact that most books forget to mention the "magic word" POSITIVE does not mean that the books are right, on the contrary, that just says that books are made by human beings and, unfortunately, the GMAT market is NOT a very careful one, because people are always writing books and new editions in a hurry, to sell a lot, compromising quality and details like this one.
@GMATGuruNY : correct!
That means that the test takers will not probably be in the "crux or spade" situation I explained to kvcpk above!!
Final remark: I have already asked the BTG manager to include me as an "Expert", but he asked me politely to keep posting for a period of approximately 2 months just to be sure I will keep contributing to this forum for a while before he evaluates my expertise... that means I would love to have "thanks" from you whenever possible, so that perhaps I will earn this "distinction" earlier, ok?!
Regards,
Fabio.