Yup

My friend did one on me about a week before I saw this post, where the lead-up questions were exactly the same, but the end question was 'think of a vegetable'. Not only did he guess my first choice, but the second one as well. He had written them down before my answer.

So the Maths doesn't have much to do with it AFAIK, it's a distraction technique to get to your subconscious, which will give the 'easiest' answer, which happens to be common amongst your 'type', for some reason.

Of course different cultures will give different answers (because they may not have those vegetables, for a start!).

Thinking about it, maybe you could ask ANY "think of a" question, and find 70% ish commonality. E.g think of a color/girl's name/etc.

I bet you were thinking of a carrot.