Some edits made...
This question is just for fun, so if it isn't fun then please feel free to ignore it. I already get a lot of help from this site so I don't want to bite the hand that feeds me. It's based on a real life example and it's just something I've wondered about a lot.
I visit my local dojo to train on an essentially random basis Monday-Friday. Let's assume I visit twice a week. This means I visit exactly twice, every week, with only the two days varying. There is one individual who is nearly always there whenever I am there. If he visits on the same day as me then I will see him. Let's assume he's there 90% of the time when I'm there. I want to know two things:
1) how often he trains
2) whether he comes on a random basis or on set days of the week.
I'm guessing perhaps we have to assume one to guess the other? I've really got nowhere with this at all. I just think about it in the warm-up every week and am baffled anew. Even if somebody gave me a way in to think about the problem I would be most grateful.