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Tue 15 Jun, 2004 09:15 am
You have ten bags of coins. Nine of the bags contain real coins, and the other contains counterfeit coins. You can tell immediately which are counterfeit, because they weigh 0.9 ounces, whereas the real ones weigh 1.0 ounce exactly. You have a digital scale, but it only has enough power to weigh something once. To use the scale you put the objects to be weighed on top, then press the "WEIGH" button. Can you figure out how to figure out which bag contains the counterfeit coins by only using the scale once?
I think I can see this, do you weigh 55 coins?
That's a classical.
You put one coin from bag 1, two coins from bag 2, 3 coins from bag 3... 9 coins from bag nine, 10 coins from bag 10.
That makes 55 coins in total.
Suppose the weight is 54.8.
55.0 - 54.8 = 0.2, you are .2 ounces short.
Then it means bag 2 has the false ones.
very nice, but I can do it with 45. How?
You don't put any coins from bag 10. If the weight of the 45 coins is 45.0 ounces, then bag 10 is counterfeit.
ah i knew that one and then blah!
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