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?"

The Answer....

[Omnieiunium]

Is obviously 42

easy one

[zanderredux]

prove that a^n=b^n+c^n for any n.

One possible solution:

[heinousjay]

Turn a light on.

Re:Riddle

[Tuxedo Jack]

None.

You haul your ass to a bakery, shell out twenty bucks, and get a box or two full of cupcakes, then you go Cid Highwind on everyone.

"Siddown and eat your goddanm cupcakes!"

Re:Oldie but goodie...

[markov_chain]

*** ZOT! ***

Re:easy one

[Anonymous Coward]

I have discovered a truly remarkable proof of this theorem that the length of this comment is too small to contain.

Re:Oldie but goodie...

[Dorothy 86]

I'm told that it depends upon the price of fish in Tibet on Tuesdays.

As I was walking to St. Ives...

[LeonGeeste]

I met a man with seven wives. Every wife had seven sacks, and every sack had seven cats, and ever cat had seven kits. Kits, cats, sacks, and wives, how many were going to St. Ives?

Re:What do you get if you multiply 6 by 9?

[Anonymous Coward]

Nobody writes jokes in base 13.

Re:Phone Numbers

[MickLinux]

Wow! It's my age! How did you do that?!?

Re:Petals of the Rose

[Damer Face]

I did 3 or 4 rolls and decided to get all intelligent at it and do some pattern analysis, so I fired up excel and solved it whilst waiting. It was something about the wording of the version I saw just gave it away.

The moral is, anything you think you need excel for can almost certainly be done quicker without.

Re:Violation of angular momentum

[NIK282000]

The spinning of the cat's tail allows it to prduce the torque needed to rotate it abotu its center of mass. That or cats are the key to free energy and antigravity *puts on tinfoil hat*

Posted @12:35AM

[Anonymous Coward]

Here's a riddle.

It's Saturday night and some geek (sorry Cliff) is desperate and dateless so he spends 3 hours composing a submission, and YES!, it gets accepted by Slashdot just after midnight.

The riddle? How sad is that?

Re:easy one

[Anonymous Coward]

I have discovered a truly remarkable proof of this theorem, but the Slashdot lameness filter won't let me post it. :-(

Re:The worm on the rubber rope...

[Harmonious Botch]

About 5 seconds after the moving end of the rope comes loose.

Re:Riddle

[akeyes]

Hmm...if the 'teenager' is 18 or 19, does that also count as an adult?

Re:Truth vs. Lies

[Hektor_Troy]

Can I switch the statue for one talking bull frog? Cause I know the answer to that one. Pick it up, open one door, throw it down that hall, close door and wait a bit.

Curtesey of The 10th Kingdom

An anecdote

[tmerrill]

John von Neumann (1903-1957) [Hungarian/US mathematician and scientist] The following problem can be solved either the easy way or the hard way.

Two trains 200 miles apart are moving toward each other; each one is going at a speed of 50 miles per hour. A fly starting on the front of one of them flies back and forth between them at a rate of 75 miles per hour. It does this until the trains collide and crush the fly to death. What is the total distance the fly has flown?

The fly actually hits each train an infinite number of times before it gets crushed, and one could solve the problem the hard way with pencil and paper by summing an infinite series of distances. The easy way is as follows:

Since the trains are 200 miles apart and each train is going 50 miles an hour, it takes 2 hours for the trains to collide. Therefore the fly was flying for two hours. Since the fly was flying at a rate of 75 miles per hour, the fly must have flown 150 miles. That's all there is to it.

When this problem was posed to John von Neumann, he immediately replied, "150 miles."

"It is very strange," said the poser, "but nearly everyone tries to sum the infinite series."

"What do you mean, strange?" asked Von Neumann. "That's how I did it!"

Re:The King and the Chalice (only for Experts!)

[brian0918]

"just so I'm sure, you can't bash the kings brains in out of frustration using the chalice, right?"

The king knows Kung Fu.

Re:Keeping my skills fresh

[sunwolf]

I keep my skills fresh by taking two points and then finding the answer we all know and love with the point-slope form!

a^2 + b^2 = c^2!

Re:Petals of the Rose

[rheotaxis]

Is it cheating to just read the JavaScript at http://www.borrett.id.au/computing/petals-j.htm [borrett.id.au] where you can play the game? I'm not saying its right, becuase I didn't know what the answer should be, so beware.

Re:0^0

[Fnkmaster]

I guess you could say 0^0 = 1, for sufficiently large values of 0. :)

Re:The best riddle site on the net

[jennifairy11]

The first prisoner takes the light bulb out of the socket and breaks it so that there are at least 99 pieces of glass. He takes all but 99 of the pieces away. Each prisoner will take one piece of glass away with them on their FIRST time. If they go twice, they don't take a second piece of glass. When there is only one piece of glass left, that person knows that everyone else has been into the room at least once and he can make his assertion.

Re:Truth vs. Lies

[Kagura]

Solvable by a human with an understanding of the context and an IQ of at least 40: Encrypted: Ner gurer gjb fgnghrf urer?
Letters by guessing: Are t ere t statues ere?
Fully decrypted: Are there two statues here?
f=s
g=t
n=a
h=u
r=e
e=r

Re:Riddle

[psmears]

When you arrive a son of the coworker answers the door. What is the probability that the other child is a girl?

<answer type="weasel">Zero—the co-worker must have two sons, otherwise the question would say "the son" rather than "a son" ;-)

Re:Boat in a lake

[oldCoder]

Yes. There are only 3 possibilities, and you've enumerated them all...

Re:Petals of the Rose

[Armchair Dissident]

Oh, I don't know about that :)

I solved it after the first roll. Here's how I did it:

1. Right-click on the window, select "View source"
2. Search for "Accept guess" in the source. Note the name of the routine called
3. Look at function, including the algorithm for the solution
4. Wait for light to dawn as to how the puzzle got its name...!

I'm not sure that's how you're supposed to solve it, but Hey - worked for me :-)

Re:The King and the Chalice (only for Experts!)

[Anne_Nonymous]

Wait a minute. Repeat as necessary.

Re:Petals of the Rose

[Tim Browse]

Unfotunately, one rumor says that the smarter you are, the longer it takes to figure out.

Max: My teacher tells me beauty is on the inside.
Fletcher: That's just something ugly people say.

-- "Liar Liar"

Re:Truth vs. Lies

[Anonymous Coward]

Thank you Captain Obvious. The point of ROT13 is not to keep you from decrypting it, it's to keep you from accidently reading the answer while casually looking at the post.

Re:The King and the Chalice (only for Experts!)

[SeanAhern]

The king knows Kung Fu.

Shouldn't that be King Fu?

-ba-dum-dum!-

Re:Petals of the Rose

[Lehk228]

the game involves throwing dice not chairs

Re:Lightbulb problem

[callipygian-showsyst]

Since I have LED lighting in my house, this won't work! And if the world switched to solid state lighting, this puzzle will be obsolete.

BTW: Donald Knuth probably hates you.