# Super hard Math for extra Credit?

So I just started school and on my first day my math teacher gave us 2 extra credit problems. They are so hard, my parents can’t even figure them out. And we haven’t covered them either so its not like I haven’t been paying attention. Can you help/explain them?

#1 Ten money bags contain silver dollars. Even though the coins look exactly the same, one of the bags is full of counterfeit coins. Genuine coins weigh 10 grams each, while the counterfeit ones weigh only 9 grams each. You have a very precise scale which will give you the exact weight in grams of whatever you put on it. The only problem is that you have to put a quarter in the slot to operate the scale, and you only have one quarter. Your task, therefore, is to figure out which bag contains the counterfeit coins in ONLY ONE WEIGHING. (You can only read one number once you put the coins on the scale and put the quarter in the slot it won’t help to add or remove bags, since the new weight will not register without another quarter.) Can you do it? If so, how? If not, why not?

so thats the first one now heres the second

#2 A string is wound symmetrically around a circular rod as shown. The string goes exactly four times around the rod. THe circumference of the rod is 4 cm and its length is 12 cm. Find the length of the string, Show all your work.

k, that sounds easy but the string is wrapped around on an angle kinda like this: http://i.ehow.com/images/GlobalPhoto/Articles/2368766/1001914-main_Full.jpg

just pretend that the little lines going diaonaly around the toilet paper roll are string. its like a calculus thing or something. we havnt done calculus ever! its college stuff! help!!!!!!

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1) take one coin from the first bag, two from the second, three from the 3rd, and so on

if the scale is 2 grams light, the second bag was counterfeit…if it is 7 grams light, it was the 7th bag