I guess the fuss(and the point this little experiment was trying to prove) is that people, when faced with seemingly simple problem like this, do not start thinking like you've just portrayed and go with the gut feeling, because the question is so seemingly simple.
To be honest the number 10 also came up immediately for me as well, then I stopped to think 'wait, there has to be more' because of the title.
And 0.10 popped into my head as well. However, the fact that this was even asked as a question would cause someone to stop and think a bit more analytically I would think.
that is a good point. Funnily enough, this is the kind of trick question which I would fall for the first time encountering, had it been asked as a quiz without any label, but the whole 50% of great students have failed labelling made me think, not doubting my answer, but doubting the difficulty of the question that I had expected.
I will need to get my introspection goggles before thinking this further.
To be honest the number 10 also came up immediately for me as well, then I stopped to think 'wait, there has to be more' because of the title.