Question

Gold coin weighs one gram, counterfeit coin weighs 1.1 grams. You have 10 bags full of coins, nine of the bags are full of real gold but one bag is full of the counterfeit coins. Given a perfect scale (a pointer scale, for example) and one weighing can you determine which bag has counterfeit coins

Answer 1

The answer is that we will take either 2 or three turns

In the first turn we will take 5 bags on each side. The lighter one will have the false bag.

Out of the five separated in the first turn we will take 2 on each side.

If they are equal then the leftover is fake.

If one side is lighter then we will measure the lighter bags on either side and hence the lighter one would be the false bag.

So we need either 2 or 3 turns. It's not possible to do it in 1 turn