Here is a brain puzzle for all you smarties.

.David.

.David.

Active member
You have 12 diamonds. They all look exactly the same the only way to differenciate them is by weight... there is a fake among them. It weighs differently.

You have a balance. You get to weigh the diamonds 3 times - however you want, and you have to figure out which is the fake.

 
it's a balance

u divide them into 3 groups of 4 and weigh 2 groups if they weigh the same then the fake is in the group not on the balance or it is in the lighter group

take that group and divide it into 2 groups of 2 and weigh again

take the lighter group and divide into 2 groups of 1 and weigh again and the lighter one is the fake then sell it to a mexican
 
well i thought of that, but i think the question means u get to weigh then ONLY 3 times. like when you weigh the 4 and then another 4, that is 2 times, u only have 1 more weigh.
 
that's assuming the fake is lighter than the real ones, or a different weight in general, which you cannot assume, because you donotknow tht for sure
 
it's a balance

you put 4 on one side and 4 on the other and go from there, kinda like a triple beam but with another platform on the other side instead of wieghts
 
Hint: you got the first step correct: divide them into 3 groups of 4. If you weight 2 groups, and they are the same, you know its in the other group you did not weigh.

continue..
 
The strength has nothing to do with it because we are pretending that they are the same strength.. the only way to figure it out is by weight.
 
yeah and brizz that works but you still dont know which one is fake. ur assuming its the lighterr one. but since you dont know this is physically impossible.

if it is heavier, you would pick the light one and have a real diamond.

still think ur close but u dont have it yet
 
A normal balance.. two platforms on either side with a balance point in the middle. Like the balance on Monty Python when they weigh the woman/witch against the duck, but smaller. :)
 
once you do 1 n 1, if they are equal, you keep 1 on and grab another 1. if those are still balanced you know the fake 1 is the remaining one not weighed.
 
Let's say that when you weigh the first two groups of 4 against each other, they are not equal.. then what?
 
you take the 3 groups of 4, weigh the 2 groups of 4 and figure out what group of 4 has the lighter weight.

take that group of 4 and weigh then 1 on 1 with each other.

so right now I have 2 weigh's left

I take 1 on the left, 1 on the right.

if they balance, I take the right side off and grab another 1 from the same group.

if these balance I then know it is the 1 I have not weighed yet.

get it
 
u switch one group with the one on the table ..... and that will tell u if the fake diamond is heavier or lighter
 
or do 6 and 6. take the one with the fake do 3 and 3, take the one with the fake and 1 and 1 with 1 one and if even the one outs fake, or the odd one on balance. that was the easiest puzzle ever
 
no no no you guys are thinking of this all wrong. You get a gun and go the guy who sold you the messed rocks. Then make him tell ou wich one if the fake. Problem solved
 
split into 3 groups of 4, and weigh 2 of the groups.

If they are the same, the it's not in that group.

Take 2 from one of the good groups and measure it against 2 of the bad pile.

If those are the same, take one of them and measure it against one of the 2 remaining diamonds...

That's 3 times if it works out that way.
 
won't work,what if the first measurement they are different? Then you have to waste a weigh determining which is the good and which is the fake.
 
she did say three things... take them into groups of 4, then 2, then one... and the lighter one is fake.... wait something clicked... unless you have luck on your side then you would only need 3... but you would most likely need at most 6 weighs to do it correctly due to varying of where the diamond is.. and plus the way you can tell if its fake is how its cut.. and how te light shines through it... its not the same as a diamond :)
 
right, I have found half a dozen ways to do it, all with 4 weighs. I can't figure out how to narrow it down to 3.
 
I know,

So....

start again.

split the 12 into 3 groups of 4..

label them 1-12

Step 1:

put 1,2,3,4 on the left side and 5,6,7,8 on the right side.

If the left side goes down goto 2a, if the right side goes down, go to 2b.

Step 2a:

put 1,2,5 and 6 on the left and 3,7,9,10 on the right side.

if the left goes down again, go to 3aa, if the right side goes down, go to 3ab.

Step 3aa:

put 1,7 on the left and 9,10 on the right.

if the left goes down - 1 is too heavy and is fake

if the right goes down, 7 is too light,

if it balances, 2 is the fake (too heavy)

Step 3ab:

Put 3, 5 on the left and 9,10 on the right.

-If the left side goes down , then 3 is too heavy.

-If the right side goes down, 5 is too light

-If it balances, then 6 is too light.

Step 2b:

place the same diamonds on the scale 1,2,5,6 on left.. 3,7,9,10 on the right

If the left side goes down, go to 3ba, if the right side goes down goto 3bb.

Step 3ba:

Put 3,5 on the left and 9,10 on the right.

-If the left side goes down then 5 is fake(too heavy).

-If the right side goes down, then #3 is fake (too light)

-If it balances, then 6 is too heavy.

Step 3bb:

Put 1, 7 on the left and 9, 10 on the right.

- If the left side goes down, then 7 is too heavy

- right side goes down, 1 is fake (too light)

- if they balance, #2 is fake (too light)
 
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