In front of you are 10 sacks containing 25 gold coins each. Each gold coin weighs exactly 1 oz. One of the sacks actually contains counterfeit gold coins. The counterfeit coins weigh 1.1 oz. Also in front of you is a penny scale. This is the type of scale that you put a penny in and it gives you back a card telling you what something weighs. The scale is accurate to .1 oz. You have one penny. Using the scale and your one penny, how do you determine which sack contains the counterfeit gold? [ May 07, 2002: Message edited by: Thomas Paul ]

Good one.. take 1 coin from the first bag, 2 from the second, 3 from the third .. and 10 from the tenth bag. Stack these coins separatly on your penny scale, plonk in your penny and measure it. The weight will be xx.yy oz if yy is 1, it means that you had 1 counterfeit coin weighing 1.1, so bag 1 is the culprit, .2 means you had 2 bad coins, so bag 2 is the culprit and so on...

Take one from first sack , two from second .... 10 from tenth If all were correct, it would weigh 1+2+... = 55 If nth sack is faulty then it would weigh 55 + .1n Now find out n