[Guest]

12 Balls, 3 Weighings: You are given 12 balls and a comparison balance. One has different weight. Can you determine which one and whether it is heavier or lighter with only 3 weighings? If so how, and if not, why not?

[Guest]

yes!

wiegh 4 against 4. if they are equal, then you know it in the final 4.

else its in the heavier group.

for the group of 4, wiegh 2 against 2, and then 1 against 1.

you can do up to 27 balls with just 1 heavy.

[Guest]

yes!

wiegh 4 agianst 4. if they are not equal then you know its in one or the other,

form here wiegh 2 heavies and 1 light against 2 heavies and 1 light.

if they are equal then its none of the balls you wieghed,

and you only have 2 lights left.

else, wiegh the the 2 heavies against one another. if they are equal then its the light from the other side.

Edited July 28, 2009 by phillip1882

[Wilson]

Think you only have 50% chance unless you now if ball is heavier or lighter from the start.

Without knowing this think it would take 6 comparison weighings to find the ball (& weight)

ps. Think this is in wrong forum.

[Guest]

Welcome to BD sourabh. This is indeed in the wrong forum though as it is not a word puzzle but a weighing puzzle. It should go under the topic "puzzles and riddles". make sure to check if this has already been done because there have been a few weighing puzzles already posted.

I think phillip has the right idea but the puzzle doesn't say the ball is necissarily heavier.

Edited July 28, 2009 by sparx1

[Guest]

Sorry , i am not aware this thing... i will post htis puzzle in other location

Thanks

[Wilson]

Think you only have 50% chance unless you now if ball is heavier or lighter from the start.

Without knowing this think it would take 6 comparison weighings to find the ball (& weight)

ps. Think this is in wrong forum.

"OUCH!"

[Guest]

Make 4 groups of three and weigh all four of them. This uses the scales twice and lets you know which group of three has the different weighted ball. You can also use these first two weighings to determine whether the last ball is heavier or lighter. So, after the first two weighings you are left with three balls. You weigh one against one. If the two balls weigh the same then the third ball is the different weight. If the balls on the scale do not match then you can determine which one it is because you determined from the first two weighings whether the ball was lighter or heavier

[rookie1ja]

Welcome to the Den, Sourabh. I have moved this thread to the appropriate forum section - New Logic/Math Puzzles.

This is one of my favorite puzzles. It is actually in the very first thread of the forum section mentioned above.

Let me direct your attention to the forum rules (see "Important: READ BEFORE POSTING" above). You will find many useful tips there - for instance, not to post puzzles which are already part of this site (you can do a quick search before you post a puzzle that you have not created).

Thread locked.