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        riddles >> hard >> 12 balls
        
(Message started by: mikedagr8 on Jul 13^th, 2007, 3:36am)

Title: 12 balls
Post by mikedagr8 on Jul 13^th, 2007, 3:36am

Guys i apologise for writing so many threads, but i am excited and want to hear other peoples responses. My answer is 4 weighs. I do this by seperating into 2 groups of 6. then selecting weighing these 2 groups. then i break this group of 6 up into 2 and measure. if the odd ball is in a group it will show. i select the odd group. then i select 2 balls and weigh. record the result then switch a ball. and record. then i look for the odd one out.

This of course is the lowest i could find, if at the second stage when i am weighing two groups of 3, adn they are equal i go to the other group and do the same.

Title: Re: 12 balls
Post by towr on Jul 13^th, 2007, 3:56am

Three is enough (http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_hard;action=display;num=1027806808;)

There's also a variation (http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi?board=riddles_hard;action=display;num=1050065099;) of the puzzle.

Title: Re: 12 balls
Post by mikedagr8 on Jul 13^th, 2007, 3:58am

does this mean i am correct? that is the smallest? because i know the variation where there is a thousand balls.

Title: Re: 12 balls
Post by towr on Jul 15^th, 2007, 8:17am

on 07/13/07 at 03:58:25, mikedagr8 wrote:

does this mean i am correct?

If three equals four, yes. I haven't checked ::)

Three weighings is enough to find the ball with different weight. With four you can also find out if it's heavier or lighter, but you don't need to know that.

Title: Re: 12 balls
Post by mikedagr8 on Jul 15^th, 2007, 5:01pm

a simple yes or no is good enough for me. But yeah, i screwed up in working out, but i knew thre answer.

Title: Re: 12 balls
Post by Aryabhatta on Jul 15^th, 2007, 6:05pm

on 07/15/07 at 17:01:55, mikedagr8 wrote:

a simple yes or no is good enough for me. But yeah, i screwed up in working out, but i knew thre answer.

If you are talking about weighing 6 balls each first, your answer is wrong.

Putting 6 balls against each other gives no information at all and is pretty useless.

And for your yes/no question, Yes, three is the correct answer and No, four is not the right answer.

Title: Re: 12 balls
Post by ehsanafshar2000 on Sep 17^th, 2007, 8:18pm

three is good