7 right well no i would think magicians would go for 8 (or maybe four) because you will try to catch me out.
i have recently started doing this trick usually to people who know i am a magician. i say "pick any number between one and ten" then i have them run through the number's out loud and just look for any little things that tip me off usually just twitches or breaks in their normal patterns as they run through the numbers eg if they blink on every number except one you know where it is.
you'd think it's just a 10 to one chance but you actually say between one and ten so if they pick either of they two you have an excuse. i also over accentuate the 10 so as to nudge them towards a high number, and tell them to keep a poker face thus making them very self concious and aware of all the little movements they make thus magnifying them. i also tell them to see it in front of them big and bright (while i put my hand right in their face so they get the visual idea) again to make them self concious of it and after a while you will get a feel for it, it is a valuable skill for all magicians to have, i currently get it to work about 50-60% of the time
did i get you right, you should try it, if it's wrong the nobody will remember it but if you get it right it might just open their mind up a little bit for your out of this world (chance zero) effect.
please try this and tell me what you think of it, as well as reporting any trends you notice like people reacting differently to them picking a "difficult number" or what ever