ok I have made myself a little excel spreadsheet which I think is right... and now I can see the probability of a repeat after n number of questions.
I make it that when you have seen 9 questions, you have 0.53 probability of having seen it before. Does this sound right?
If so how do I convert this into the number of questions would I have to answer on average before I get a repeat?
Is it just the number at which the probability hits 0.5?