You have to be careful with this achievement. For the answers to count as correct, it must be the first time you're given the question. If you don't receive experience from it, then it doesn't count.
Best way to do this is to start a fresh playthrough (you can go for the complete the game on hard achievement) and use a guide for any that you're unsure of. Here's a link to a guide with all the answers:http://www.gamefaqs.com/console/xbox360/file/932586/45614