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Brain Teaser - Gold Coins

In this video, Mahalo math expert Allison Moffett gives you a brain teaser question.Brain Teaser---------------------------------------------------------------------You have 10 bags filled with 1,000 coins each. One bag is filled with forgeries. A true coin weighs one gram while the counterfeit weighs 1.1 grams. If you have an accurate scale which can only be used once, how can you identify the bag with the forgeries?The Correct Answer---------------------------------------------------------------------There may be multiple ways to solve this problem, so if you found one that works, great job! If not, keep trying or read on to find out one way of solving it.You can start by numbering each of the bags one through 10. Then take one from the first bag, two from the second, three from the third, four from the fourth, five from the fifth, six from the sixth, seven from the seventh, eight from the eighth, nine from the ninth and 10 from the 10th.Weigh all of these coins. Since you are weighing 55 coins, if they were all authentic, it would weigh 55 grams. But since some of them weigh a tenth of a gram more, whichever bag has the counterfeit coins will contribute that much more weight.For example, if the seventh bag had the fake coins, the weight of all the coins you set aside would be 55.7 grams. Thus whatever number comes after the decimal point is the number of the bag with the fake coins.If you've found another way of solving it, let us know at [email protected] Happy solving!Read more by visiting our page at:
Length: 01:11


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