Riddle Me This: Weighing Fake Coins

You can find the counterfeit coins with only one weighing. Because you know that the real coins weigh an ounce each and the counterfeit coins weigh half an ounce each, this is what you can do:

Take one coin from the first group, two coins from the second group, three coins from the third group, and continue in this fashion until you get to the tenth group which you till take in its entirety. You will have fifty-five coins total, and when you place them on the scale it would read 55 ounces if all of the coins were real. Because you have taken a sample from each group you know that the scale will read less than that. If the scale reads 54.5 ounces you know that there is one counterfeit coin in the group, so you know that the group of counterfeits is the first group which you took a sample of only one coin from. If the scale reads 54 ounces you know there are two counterfeit coins on the scale, so it must be group two. This way of weighing will lead you directly to the stack of counterfeits.