Maths puzzle three

[EddieM]

There is a pile of twelve coins, all of equal size. Eleven are of
equal weight. One is of a different weight. In three weighings find
the unequal coin and determine if it is lighter or heavier.

 

[EFLImpudence]

Have we scales - or just able to weigh one lot at a time?

 

[EddieM]

We have a balance, yes.

 

[EFLImpudence]

I'm cunfused by not knowing if the odd one is heavier or lighter.

 

[EddieM]

I'm cunfused by not knowing if the odd one is heavier or lighter.

That you have to determine. It is not given.

 

[SammyInnit]

Divide the 12 coins into 4 piles of three, put 2 of each of the piles on each side of the scale (weigh 1)

Out of the heaviest 2 piles, put each pile of 3 back on the scales (weigh 2)

Out of the three heaviest coins, you'll either have 2 perfectly balanced or one will be heavier, tipping the scales (weigh 3)

Bit stuck on how to determine which has the true weight if you're left with two odd coins on the scales.

 

[EddieM]

Divide the 12 coins into 4 piles of three, put 2 of each of the piles on each side of the scale (weigh 1)

Out of the heaviest 2 piles, put each pile of 3 back on the scales (weigh 2)

Out of the three heaviest coins, you'll either have 2 perfectly balanced or one will be heavier, tipping the scales (weigh 3)

Bit stuck on how to determine which has the true weight if you're left with two odd coins on the scales.

Close'ish

 

[EFLImpudence]

Out of the heaviest 2 piles, put each pile of 3 back on the scales (weigh 2)

That's the problem, isn't it? The odd coin might be lighter and so in the lighter piles.

 

[SammyInnit]

That's the problem, isn't it? The odd coin might be lighter and so in the lighter piles.

Yeah, without knowing if it is heavier or lighter it's all a guess.

 

[Ian H]

Put a pile of 2 on each side of the scales 3 times. Which ever pile of 2 is higher/lower contains the odd coin.

Take them off the scale and feel which is different.