Logic Puzzle

You have 10 stacks of 10 coins each. One stack is composed of coins that weigh 0.9 grams each. The other 9 stacks are composed of coins that weigh 1.0 grams each. If I gave you a scale that was accurate to 0.1 grams, how could you determine with a single measurement of any number of coins from any number of stacks, which stack contained the 0.9 gram coins?

Answer to the last Logic Puzzle:

C = chickens
E = Eggs
D = days
1.5 C * 1.5 D = 1.5 E
2.25 ( C * D ) = 1.5 E
C * D = 1.5 * E / 2.25

In other words, one chicken produces 2/3 of an egg per day, so in 3 days, a single chicken would produce 2 eggs.