If you have a grandfather from India, a grandmother from Ireland and a grandfather on the other side also from Ireland, and finally a grandmother from China, you're 1/4 Indian, 1/2 Irish, 1/4 Chinese, and 100% confused.
For the purposes of this question, assume that if you go far enough back you'll end up with all of your ancestors 100% something or other -- there's no such thing as saying that when the great country of Zombihahoo split up, that everyone was suddenly considered 2/3 Zombish, 1/6 Haheesh, and 1/6 nothing at all. Or saying that a woman who isn't sure whether the father is Guido the Italian, Bonzo the Lithuanian, or Hiro the Japanese can declare her child to be 1/6 each.
A child is always 1/2 what the mother was and 1/2 what the father was.
Part 1: Is there any way to be *exactly* 1/3 German?
Part 2: Can you explain why or why not, without using any mathematical symbols or terminology that an 8th grader would be unfamiliar with?
Part 3 (this is the real question): Now say you allow time travel. As in, your son can go back in time and screw your great grandmother, so that your son *is* your great grandfather. Does this change the answer to part 1? Why or why not?
I'll screen all comments and remove the spoilers, but I'll also say whether you got it right. Or at least, if you agreed with my answer. So don't worry about giving anything away.
Update: My apologies, but it seems Livejournal only allows me to accept or reject whole comments; I cannot edit them to remove spoilers as I intended. So I think I'll hold everything in moderation until Wednesday, then display all comments unmodified (and stop moderating comments, in case you want to discuss). For the record, there are currently 9 responses, with 9 wildly varying explanations in part 2. I especially like the one that begins with "That should be easy. I just finished 8th grade and I'm on my summer vacation." For part 3, there's some debate about what time travel can or cannot do, so people are kind of falling on both sides of it depending on their opinions about time travel. My favorite there would have to be "But I don't think time travel works this way."
Update 2: bz pointed out to me that Livejournal forces you to watch an ad before posting a comment. Argh! So, I am now also soliciting suggestions for a new blog hosting service. I could just use github, but I'm not sure how it deals with comments.