Riddle

[Batman]

4Q All.

There are five bags of gold that all look identical, and each has ten gold pieces in it.

One of the five bags has fake gold in it.

The real gold, fake gold, and all five bags are identical in every way, except the pieces of fake gold each weigh 1.1 grams, and the real gold pieces each weigh 1 gram.

You have a perfectly accurate digital gram scale and can use it only once.

How do you determine which bag has the fake gold?

Ok I think I have it but I could be way off you take 1 coin from the first bag 2 coins from the second 3 coins from the 3rd etc, depending on how many .1 grams it is over would tell you which bag is the fake gold...does that make sense?

So if the total ways .3 grams over then you know that is fake.

It works in my head

Right O, I can try and explain this a bit better now I'm on my laptop and not on my phone

so...

bag 1 - 1 coin
bag 2 - 2 coins
bag 3 - 3 coins
bag 4 - 4 coins
bag 5 - 5 coins

all get weighed at the same time so you are only using the scales once (not adding or removing weight as the other posts suggested)

so if they were all real gold you would have 15 grams total

however many 0.1 grams it is over by will show which bag is the fake, so for example if you have 15.3 grams then you know that the 3rd bag is the fake, 15.5 and you know that the 5th bag is the fake