Bit harder problem

[swidders]

12 balls - all identical in every way apart from one which you are told weighs a different amount by a tiny fraction.

You are allowed to use a set of balancing scales three times only, at the end of which you will be able to determine which is the odd ball out and whether it is heavier or lighter that the others.

How do you go about doing this?

 

[WDIK]

weigh 12 balls 6 and 6

discard the 6 heavier

weigh 3 and 3

discard the 3 heavier

weigh 2 balls 1 and 1

either one ball is lighter than the other, or the scales balance.
then the ball not weighed is the lighter one.

 

[swidders]

weigh 12 balls 6 and 6

discard the 6 heavier

Why? You don't know that it's not heavier.

 

[WDIK]

weigh 12 balls 6 and 6

discard the 6 heavier

Why? You don't know that it's not heavier.

Mr picky you are a fiend, darn you sir

 

[WDIK]

curses, damn your eye's sir.

it can only be done in 4 moves, 3 with only a 50% chance of being right

 

[blondini]

it can only be done in 4 moves, 3 with only a 50% chance of being right

It really can be done in three moves, 100% accurate guaranteed.

 

[peteftw]

this is the three weighings problem even when the answer is explained to me i still dont get it.

you could find the odd one out in 120 balls with 5 weighings apparently

 

[sooey]

Place them in the scales 6 and 6, obviously they won't balance so remove 3 balls from each scale. If they then balance discard the balls in the scales and replace with previously removed balls 3 and 3, this then becomes your second go. Remove one ball from each scale and place to one side, if they then balance it must be one of the just removed balls, in which case use your third go to weigh one of them against any other ball. Which will tell you the odd one out. If on your second go, the scales don't balance after removing one from each, simply remove another one from each scale.

 

[WDIK]

simply remove another one from each scale.

yes but you dont know if the odd ball is heavier or lighter

 

[sooey]

simply remove another one from each scale.

yes but you dont know if the odd ball is heavier or lighter

Of course you would, if the right hand scale was lower then the ball from that side is heavier etc. etc.

 

[WDIK]

simply remove another one from each scale.

yes but you dont know if the odd ball is heavier or lighter

Of course you would, if the right hand scale was lower then the ball from that side is heavier etc. etc.

you have no point of reference

 

[tim west]

The problem in flash format:

http://www.novelgames.com/flashgames/game.php?id=4

SPOILER WARNING

be careful there is a link to the solution on the start page

 

[noseall]

it has been done before on this very forum......//www.diynot.com/forums/viewtopic.php?t=56702

 

[swidders]

The problem in flash format:

http://www.novelgames.com/flashgames/game.php?id=4

SPOILER WARNING

be careful there is a link to the solution on the start page

it has been done before on this very forum......//www.diynot.com/forums/viewtopic.php?t=56702

I am disappointed that to try and solve it some of you are looking for previous solutions.

 

[sooey]

you have no point of reference

I think I do, although I don't seem to be explaining it very well.