12 coins by engiin!!

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Wide

#367399 Sat, 19 May 07 09:33 AM

there are 12 coins.one of them is false; it weights differently.it is not known , if the false coin is heavier or lighter

than the right coins.how to find the false coin by three weighs on a simple scale?

Wide

Joined on Tue, May 8 2007

turkey

New Member (24)

hi everyone.

Pucca

#367470 Sat, 19 May 07 01:02 PM

Maths? Probability? Stick out tongue [:P]

Pucca

Joined on Sun, Aug 27 2006

Senior Member (2,935)

¿Alguna vez has tenido un sueño tan real que al despertarte no sabías qué creer?

Golden

#367626 Sat, 19 May 07 06:57 PM

there are 12 coins. = 12 coins

one of them is false; so 1-12 = 11.

11 coins of same weight
1 is not

how to find the false coin by three weighs on a simple scale? (i don't understand)

Golden

Joined on Wed, Feb 8 2006

don't want to tell

Full Member (184)

For those who accept their fate find happiness, those who defy it, glory. - Princess Tutu

Pucca

#367633 Sat, 19 May 07 07:14 PM

Maybe he wants to know the probability of taking that false coin in three attempts Smile [:)]

Pucca

MrPedantic

#367723 Sun, 20 May 07 12:13 AM

Yes; you have 12 coins, one of which has a different weight from the other 11. You also have a balance. How do you detect the odd coin out, using the balance only 3 times?

MrP

MrPedantic

Joined on Tue, Oct 12 2004

Veteran Member (12,231)

...opella forensis / adducit febris...

Pucca

#367757 Sun, 20 May 07 02:12 AM

But we still need something else! Do you return the coins you take out to the "box" or not? Smile [:)]

Pucca

Anonymous

#367771 Sun, 20 May 07 03:42 AM

wouldn't the odd coin look different? it would be thinner or fatter than the rest if it's lighter/heavier.

Anonymous

Grammar Geek

#367799 Sun, 20 May 07 05:33 AM

I think to do it in three, you need to know if it's heavier or lighter, not just "different."

Let's assume lighter.

Take any four and put it them on one side of the balance, and any other four and but them on the other.
- If it balances, the odd coin is one of the four not yet weighed.
- If it does not, you'll know which set of four the lighter coin is in.

You should be able to figure out what do to from there.

But if you don't know if it's lighter or heavier, you will need at least one more round of weighing.

Grammar Geek

Joined on Tue, Jan 10 2006

Pennsylvania, USA

Veteran Member (16,603)

Barbara, who answers in American English.

MrPedantic

#367943 Sun, 20 May 07 12:44 PM

You don't need to know if it's lighter or heavier, to do it in three; but it is a horribly complicated procedure, with several "if this, do X, but if that, do Y" branchlets.

(In other words, it isn't one of those "Why didn't I think of that?" solutions.)

MrP

MrPedantic

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