There are five identical looking bags of gold coins.  Four of the bags contain coins made of real gold and one of the bags contains coins made of fool’s gold.

All of the coins in all of the bags look identical.  They are the same size, color and shape. The only difference is their weight. Real gold coins weigh 10 grams and coins made of fool’s gold weigh 11 grams.

You have an accurate scale that you can use only one time to determine which bag contains the fool’s gold.  How do you do it?