The first part, I know you have to take different numbers of coins.
But the 2nd part, I had to look at the answer.

Very well done.

>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.
>>>>>