tea.mathoverflow.net - Discussion Feed ("A counting problem")

Gerry Myerson comments on ""A counting problem"" (10228)

2010-11-05T15:08:26-07:00

David, nobody called the question in question homework. It's possible that those who voted to close thought it was homework, but we don't know that. Moreover, there are other reasons that might prompt someone to vote to close, which I'll summarize by saying that the proposer didn't do enough to "sell" the question. This is one of many cases in which I wish that those who vote to close a question would leave a comment as to why.

Having said that, I, too, have been surprised at seeing some other questions tarred with the homework brush, questions which, when I looked at them carefully, seemed to be well beyond the homework level.

And having said that, I think it's going to take me a lot of work to see how to get to an answer from the hints you posted, but I'll have a go at it.

Ryan Budney comments on ""A counting problem"" (10205)

2010-11-05T09:36:13-07:00

If there's no further discussion about the appropriateness of this question perhaps we should flag it for a moderator to close.

David Speyer comments on ""A counting problem"" (10202)

2010-11-05T07:32:37-07:00

The more I think about this, the more I think this is solidly below what we want on MO. I probably jumped too soon to reopen.

David Speyer comments on ""A counting problem"" (10200)

2010-11-05T07:19:49-07:00

Okay, now that I have an answer, I'm not sure whether this was worth reopening or not. It does yield to standard linear recurrence techiniques, it just takes skill to apply them here. I guess my feeling is that this might be a good question, if asked with motivation by someone who just happened not to have taken a good combinatorics course. I wish people wouldn't describe this sort of thing as homework. Oh well, I can't unreopen, so I'll go post some hints in the comment thread.

David Speyer comments on ""A counting problem"" (10193)

2010-11-05T07:03:17-07:00

I just cast the reopening vote, because I don't see how to do this. I'm not saying I couldn't do it if I sat down for an hour and played with it (and maybe I will), but I can't immediately think of any approach which lets me control both the number of balls of each color, and the number of sign changes.

(UPDATE: Okay, I see how to do it. I could imagine assigning this with some hints, but it still strikes me as too hard to be a homework problem without hints. I'm skeptical that the 5 close voters actually saw how to do it.)

I am confused at people's willingness to call a question homework. I have a reputation for assigning overly hard problem sets, and I would never assign most of the problems that get labeled as homework here.

jbl comments on ""A counting problem"" (10187)

2010-11-05T06:09:28-07:00

http://mathoverflow.net/questions/44772/a-counting-problem-closed

Lots of discussion about the propriety of the question happening in comments. I'm creating this thread so any future discussion can happen here.

I think Gerry's comment "gondolf, this looks like a problem at the level of an undergrad intro combinatorics class. Maybe there's more to it than that - can you convince us? Say, show us that you've tried some pretty sophisticated approaches that didn't work? Or that you have some reason for wanting the answer unrelated to a class you're enrolled in?" is the key one for determining whether this thread should be re-opened.