# The Naked Scientists Forum

### Author Topic: The odd ball puzzle have you attempted it yet?  (Read 251 times)

#### Alan McDougall

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##### The odd ball puzzle have you attempted it yet?
« on: 09/06/2016 02:34:42 »
This problem has appeared in several collections of mathematical brain-teasers and from time to time gets resurrected to challenge yet another generation of puzzlers.

The problem can be stated as follows. We arc given twelve balls, identical in appearance but one of which is a tiny bit either heavier or lighter than the other eleven.

We are allowed only three weighings with a balance scale, to determine which is the odd ball and to find whether this ball is heavier or lighter than the others.

Give it a go?

Alan

Balance scale like the one often seen in a court of law, of course you do not need an actual balance scale just imagine it.

You can get the solution on the internet but that would spoil it for those who want to solve it on their own bat, so to speak?

#### chiralSPO

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##### Re: The odd ball puzzle have you attempted it yet?
« Reply #1 on: 09/06/2016 16:56:51 »
This is a trivial problem, but I will not spoil it here for those who have not thought about it before...

HINT: you can only get useful information when there are equal numbers of balls in each of the dishes of the balance, but because of the way the problem is set up, you can still get information about balls that are NOT in the dishes...

#### Thebox

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##### Re: The odd ball puzzle have you attempted it yet?
« Reply #2 on: 09/06/2016 17:39:04 »
This problem has appeared in several collections of mathematical brain-teasers and from time to time gets resurrected to challenge yet another generation of puzzlers.

The problem can be stated as follows. We arc given twelve balls, identical in appearance but one of which is a tiny bit either heavier or lighter than the other eleven.

We are allowed only three weighings with a balance scale, to determine which is the odd ball and to find whether this ball is heavier or lighter than the others.

Give it a go?

Alan

Balance scale like the one often seen in a court of law, of course you do not need an actual balance scale just imagine it.

You can get the solution on the internet but that would spoil it for those who want to solve it on their own bat, so to speak?
Ok, I think it must be a process of elimination and if there is 12 balls and we have three attempts we must work out firstly some numbers, if we weighed 2 and 2 that would be three attempts and we could narrow it down to 4 balls, so that must be the wrong number, oh eke my head hurts already this will keep me good, hmmmmm, pause,  I can see the answer but just got work out the order, pause, if we weigh 3 and 3 we could determine which six with only one attempt, a second attempt we could 2 and 2 To determine which four although we could get lucky and only have 2  if the 2 and 2 balance, grrrrr am I close .?

#### The Naked Scientists Forum

##### Re: The odd ball puzzle have you attempted it yet?
« Reply #2 on: 09/06/2016 17:39:04 »