If I line up all the bags in a row and consider the bags as bag 1, bag 2 and so on.
If I take 1 coin from bag one
and 2 coins from bag two
and 3 coins from bag three
and continue for all twenty bags
and pile them neatly on the scale being carefull not to mix them up
I will have twenty piles of coins from 1 coin to a pile of twenty coins
I will have 210 coins on the scale if they were all fake they will weigh 10% less than 210 onces or 189 onces. Now if I use the penny and find the actual weight is somewhere between 189.1 for bag one and 191 onces for bag twenty.
Let's say it weighs 190.9
I would subtract 189 from 19.9 and have 1.9 onces and multiply that by 10
The answer would be bag 19
If you would like to see the answer to this riddle highlight the white space above this message.