I've seen this or similar problem before. Cannot say for sure. I only remember that you've to take different # of coins from each bag to solve it. :)

>That was very fast.
>I couldn't solve this one on my own.
>
>Have you heard of this problem before?
>
>>

Take the following # of coins from the bags:
>>(1+2+4+8+16+32+64+128+256+512) * 1.2 = 1227lb
>>The weight difference (WD) = 1227lb - Actual weight
>>If WD >= 51.2 than 10th bag holds fakes. WD = WD - 51.2
>>IF WD >= 25.6 than  9th bag holds fakes. WD = WD - 25.6
>>...
>>IF WD  = 0.1 than  1th bag holds fakes.
>>

>>
>>>That's a different solution than I used but works in the same way.
>>>Now how about part 2?
>>>
>>>>Take 10 coins from the first bag, 20 from the second, ..., 100 from the tenth and put on scale. Substract weight from 660lb and you'll get bag # with fake coins.
>>>>