I was at a local pub last night & one of the waiters hit me with this riddle. Well maybe it’s more of a puzzle, but anyway it made me think a bit. Took me a little while but I’ve got it figured out.
Anyway, it goes like this:
You got eight marbles, all the same size & weight except for one that is heavier. You’ve got a scale that has no measurment markings on it. It’s one of those two sided scales. You can only take two readings from the scale & your task is to determine which marble is the heavy one.
I’d put four in each pan and see which side was heavier. Ditch the four “light” ones. Now you have four, one of which is the heavy one. Put two in each pan. The heavier side is holding the big one and one light one. Now–this depends a lot on how the riddle was worded, but could you then remove a marble from each side for a reading #2 1/2? You aren’t really adding a whole new set, but if you removed a marble from each side and the scales even out–you’re holding the heavy one in your hand. If they’re imbalanced, the heavy one is still in the pan.
Without sneaking in that last reading though, I’m not sure how to determine the heaviest from the two left after reading #2. I’m sure someone will be along soon with a simpler answer that makes me look like a twit.
It took me about 45 seconds to get it (if I’m right).
1.) put three marbles on each side of the scale. If they’re even, then it’s one of the two remaining marbles and you can find the heavy one with your remaining measurement.
2.) if one set of three is heavier, then weigh any two of those three. It’s either one of those two, or the remaining one.
Too easy.
Try this.
XIII + I = XI
Imagine that the equation is made entirely of matchsticks. Make the equation true by moving just one matchstick.
OOh! Maybe one of youse guys can figure this one out for me! You’re standing at a fork in the road, and there is a man standing there. One fork in the road leads to the Valley of Lies, where everyone lies all the time, and the other to the Valley of Truth, where everyone tells the truth all the time. You want to go to the Valley of Truth. You get to ask the man one question to find out how to get there, but you don’t know which valley he’s from. What one question do you ask him?
I used to know the answer to this, but I forgot and it’s been bugging me now for close to 20 years.
How about the same marble question, but you are allowed three weighings, there are 12 marbles, and one is either heavier or lighter. You must determine which is different, and how it is different.
The one from the Valley of Truth would point to the fork that leads to the Valley of Truth, for he cannot lie (and perhaps he likes big butts, but that’s another matter).
The one from the Valley of Lies would point to the fork that leads to the Valley of Truth, for he cannot tell the truth.
In each case, they point out the way to the Valley of Truth - you don’t even need to know whether the guy is a liar or not.
My favorite variation on this theme is to ask “Did you know that they are giving away free beer in the Valley of Truth?”
The Truth-teller will say “No” and then quickly run down the path to the Valley of Truth to get him some free beer - the Liar will say “Yes” and run down the path…
Oh, okay. It’s the pointing that I didn’t factor into it; I just thought they would say “Truth” and I’d have used up my question without knowing which one was Truth.
You have 13 balls, 4 red, 4 pink, 4 blue, and 1 black. You mix up the balls and fit them into three urns: a green, a yellow and a white urn. You then weigh the urns on a set of perfectly balanced scales, but you are limited to two weighings. How do you determine which urn could be carried by a swallow migrating south?
That’s why you don’t ask “In which valley do you live?”, but you DO ask “Which road did you take to get here?”. The indicated road will always lead to the Valley of Truth. It’s not necessarily pointing, it’s all in the phrasing of the question. A potential answer could be “The left road”, or somesuch.
