Maybe this is the right place to ask. I've tried to anwer this one: math.stackexchange.com/questions/387974/colored-balls-puzzle by giving a link to the same question on MathOverflow. But it was automatically converted to a comment. What should be done now?

@azimut The software thinks that when a question can be answered with a link to another question, it's a duplicate. But we can't close it as a duplicate because the other post is on a different site. My suggestion: repeat the main points of the solution that Russ Woodroofe gave on MO (copy and paste the relevant part), and consider including the improvements from the comments to that answer. With attribution, of course.

Actually, the point is moot now because another user answered the question before noticing your comment. Oh well.

Another question answered on MO #89107. If you have the standard text "Please consider converting your comment into an answer..." in your buffer, could you please paste it there? It may help if it could be visible on the chat page permanently - e.g. you could post it in this chat, then we will add stars.