Well, it turns out that most of the time people don't read the full question. For a touch of fun on Goodreads I used the quizzes feature to create a 'Monsters of Fiction' quiz focusing on ghosts, ghouls, orcs, orges, Dracula and so on. Out of interest I created a question on Scrooge with the actual phrasing being 'How many ghosts visit Scrooge and speak with him?' To which I had the answer as 3.
So many people helpfully pointed out that indeed, as I was aware, 4 ghosts visit Scrooge, and my answer was therefore wrong. However, note that my question was not 'How many ghosts visit Scrooge?' My question was 'How many ghosts visit Scrooge and speak with him?' To which I reply that only 3 speak with him as the ghost of Christmas Future never speaks. However, after the hundredth or so response to this question being 'you're wrong' from well wishers I have altered my phrasing so it no longer is a trick question to 'how many ghosts speak with Scrooge?'
In all of this I had resolved to keep the question up as a test to see how many people read the full question. Clearly, very few do. Fewer still read down to see if perhaps this answer has already been resolved in the comments thread attached. The moral of the story is that even among readers there are many subtleties that can be missed. I do not say this to belittle anyone but more as an interesting comment on how intent can be subtly changed by a little change in phrasing.