Your Favorite Math/Logic Riddles?

shma asks: "Whether you're involved in the Sciences, Mathematics, or Engineering, you undoubtedly enjoy finding simple solutions to seemingly difficult problems. I'm sure you all have a favorite mind-bender, and who better to share it with than the Slashdot community? Post your own problems and try to solve others. Just one request: If you have figured out the solution, link to it in a post, rather than write it out where anyone can see it." What brain benders tickle your fancy? "Here's a sample to consider: You're in a dark room with 50 quarters, 18 of which are heads up. You are allowed to move around the coins or flip some or all of them, if you wish. Problem is, it's too dark to tell what you're moving or flipping (no, you can't figure it out by touch either). Your job is to split the coins into two groups, each of which has the same number of heads up coins. How do you accomplish this?"

Comments

Look and Say

[Noksagt]

There's a good write up of this on MathWorld.

Re:easy one

[NitsujTPU]

Uhmm, if n = 0, that is not true.

a^0 = 1
b^0 = 1
c^0 = 1

1 != 2

So, I would submit that that might be true for all nonzero values of n.

Re:easy one

[calvin1981]

Well, If b=0, b^0 is not even defined ! For n=0, it is easy to see that there is no solution. For n smaller than 3, it is elementary to show that there are solutions (even infinitely many of them), and for n > 3, you have to be Andrew Wiles to show that :)

Except...

[nwbvt]

Dividing by zero is not "perfectly valid algebra". Division is not closed on the set of real numbers. Its not really a riddle if you lie in the problem description. Otherwise the solution to the sample problem could be "Pull out 9 of the quarters into a seperate group. I was lying when I said you couldn't see any of them."

MOD PARENT TROLL

[LeonGeeste]

I had a conversation with Brian0918 on AIM this morning, in which he revealed he's really trolling when I pointed out to him there is no solution (see my other posts) on this topic. Here's a little tidbit: ". i usually just post the problem to get people into big disputes, which so far has worked 2 out of 2 times". If you want the full conversation, email me at sbartaNOSPAM_at_MAPSONgmail.com.