``` wu :: forums (http://www.ocf.berkeley.edu/~wwu/cgi-bin/yabb/YaBB.cgi) riddles >> hard >> Coin weghting: 13 coins with  2 defected coins (Message started by: wonderful on Apr 3rd, 2008, 4:45pm) ``` Title: Coin weghting: 13 coins with  2 defected coins Post by wonderful on Apr 3rd, 2008, 4:45pm I posted the same question in the "easy" section a a follow-up to Hippo's correct answer for the case of 8 coins. That said, it might be more relevant to post this question here: There are 13 coins of which 11 weighs A g each. The other two are defected. One weighs (A+ 2) g and the other weighs (A-2) g. Can you find out the two different coins using minimum weightings? Have A Great Day! Title: Re: Coin weghting: 13 coins with  2 defected Post by Grimbal on Apr 4th, 2008, 6:00am Are these weightings on a 2-pan scale or on a scale that gives the weight? Title: Re: Coin weghting: 13 coins with  2 defected Post by Hippo on Apr 4th, 2008, 1:11pm I expect its the same puzzle with 8 replaced by 13, so the 2pan scales are expected.So for the start there is 34<13*12<35 initial positions so we are trying to find solution on 5 measurements. Title: Re: Coin weghting: 13 coins with  2 defected coins Post by wonderful on Apr 4th, 2008, 9:14pm [hide]5 is the correct answer.[/hide] Next, we would like to design a weighting scheme to achieve this target. Result from the 8 coins can be used here.Have A Great Day! Title: Re: Coin weghting: 13 coins with  2 defected coins Post by wonderful on Apr 14th, 2008, 2:31am It has been a while and it seems that nobody has come up with a solution. As such, I would like to give some hints here:[hide]In the first three weighting we can do something like this:(5, 6, 7, 8)  ?  (9,10,11,12)(2, 8, 11, 12) ?  (3, 4, 9, 10)(1, 4, 6, 10) ? (3, 7, 9, 12)[/hide]After that, there are two more weightings.Let's continue.Have A Great Day! Powered by YaBB 1 Gold - SP 1.4! Forum software copyright © 2000-2004 Yet another Bulletin Board