Much much tougher brain teaser - Page 2

Stuey · #1 08-09-2005, 04:04 AM

you can only use the scale 3 times.

So if you weigh the first 2 piles of 4 rocks and they are not equal your methods fails. If you get lucky and they are equal it works though. Good chance I'm blowing smoke here. [img]/images/graemlins/blush.gif[/img]

Luzion · #2 08-09-2005, 04:07 AM

[ QUOTE ]
Separate the rocks into 3 equal piles of 4. Weigh each, the odd one out contains the different rock (rock X). This also will tell you if it is lighter or heavier and the weight of each individual other rock (Y).

Take two rocks from the group you now know contains rock X and weigh them. If they weigh 2Y, take one of the two remaining rocks and weigh it. It is either X or a Y.

If they don't weigh 2Y, pick one and weigh. It is either X or a Y.

Obviously if the rock weighs Y, the other rock is X and vice versa.

[/ QUOTE ]

Wait wait wait... I want to clarify something.... What kind of scale are we using? Are we using something that weighs the thing you put in it? Or are we talking about a scale like this...

chuddo · #3 08-09-2005, 04:30 AM

this puzzle is only solvable in 3 steps when using a balance scale.

and it is not too tough, but a bit fun.

separate into 3 piles of 4 rocks: A, B, and C

assume odd rock is light.

Place A and B on the balance. if balance = even, odd rock is in pile C. if uneven, odd rock is obviously on the lighter scale.

you now have a group of 4 rocks and one is odd, and can use the balance scale two more times.

Seperate this group of 4 into 2 groups of 2 stones: D and E.

again, lighter side contains the odd rock.

finally take these last 2 rocks, balance them on the scale. lighter rock is obviously the odd rock of the 12.

battschr · #4 08-09-2005, 04:33 AM

[ QUOTE ]
this puzzle is only solvable in 3 steps when using a balance scale.

and it is not too tough, but a bit fun.

separate into 3 piles of 4 rocks: A, B, and C

assume odd rock is light.

Place A and B on the balance. if balance = even, odd rock is in pile C. if uneven, odd rock is obviously on the lighter scale.

you now have a group of 4 rocks and one is odd, and can use the balance scale two more times.

Seperate this group of 4 into 2 groups of 2 stones: D and E.

again, lighter side contains the odd rock.

finally take these last 2 rocks, balance them on the scale. lighter rock is obviously the odd rock of the 12.

[/ QUOTE ]
Why can we assume that the odd rock is light?

Luzion · #5 08-09-2005, 04:33 AM

[ QUOTE ]
this puzzle is only solvable in 3 steps when using a balance scale.

and it is not too tough, but a bit fun.

separate into 3 piles of 4 rocks: A, B, and C

assume odd rock is light.

Place A and B on the balance. if balance = even, odd rock is in pile C. if uneven, odd rock is obviously on the lighter scale.

you now have a group of 4 rocks and one is odd, and can use the balance scale two more times.

Seperate this group of 4 into 2 groups of 2 stones: D and E.

again, lighter side contains the odd rock.

finally take these last 2 rocks, balance them on the scale. lighter rock is obviously the odd rock of the 12.

[/ QUOTE ]

What the hell man... the hard thing about this puzzle is NOT KNOWING if the rock is gonna be heavier or lighter then the other 11 rocks...

Anyone couldve solved it if we already knew ahead of time if the rock was heavier or lighter then the other rocks

chuddo · #6 08-09-2005, 04:36 AM

blah, im a donkey. didn't take note of the fact you have to devine whether or not the stone is lighter or heavier relative to the other stones while finguring it out.

this makes the problem much more challenging, but you can see that the partial algorithm in my last post is a piece of it.

i just worked it out and now think this is a good puzzle, and will leave the final solution out so others can work it out.

PorscheNGuns · #7 08-09-2005, 10:19 AM

chuddo Im pretty sure you dont have jack [censored] worked out

-Matt

deadmoney98 · #8 08-09-2005, 05:02 AM

[ QUOTE ]
Separate the rocks into 3 equal piles of 4. Weigh each, the odd one out contains the different rock (rock X). This also will tell you if it is lighter or heavier and the weight of each individual other rock (Y).

Take two rocks from the group you now know contains rock X and weigh them. If they weigh 2Y, take one of the two remaining rocks and weigh it. It is either X or a Y.

If they don't weigh 2Y, pick one and weigh. It is either X or a Y.

Obviously if the rock weighs Y, the other rock is X and vice versa.

[/ QUOTE ]

[ QUOTE ]
that's more than 3. that's like 5.

[/ QUOTE ]

Wow, I am dumb at 4 AM, sorry about being an idiot.

Josh W · #9 08-09-2005, 04:03 AM

Is it a scale like "this weighs 10 lbs."? Or a balance like "this side weighs more than that side"?

Josh

milliondollaz · #10 08-09-2005, 04:18 AM

if you know if it's heavier or lighter...

1. you split the group into two and weigh (compare) them.
2. if odd stone is heavier, you take the heavier 6, if it's lighter, you take the lighter 6, and split them into two groups of three, and weigh them.
3. you take the three stones that are heavier (lighter) and you weigh just two of them.

it will be obvious if one is heavier (lighter). if they balance, the one in your hand is heavier (lighter).

still can't figure out how to do it if you don't know if it's supposed to be heavier or lighter. cause you could get the first step wrong and split up a group of evenly weighing stones, and you would need another step fix your wrong initial guess...