You have ten bags of identical gold bars. Every bag contains at least ten bars of gold. You find out that someone replaced every bar of gold in one bag with counterfeit gold bars. The only difference between the gold bars and the fake bars is the weight. Every gold bar weighs exactly one pound (16 ounces). Every counterfeit bar weighs exactly 17 ounces.

You are allowed to use a regular scale exactly once. The scale is accurate, and can hold all of the bags of gold at once. How can you use one weighing to figure out which bag contains the counterfeit bars.

• We don't know how much the bags weigh, so don't put the bags on the scale.
• In other words, you may open the bags
• You don't have to put all the bars on the scale
• Why don't you put ten different piles of gold bars on the scale?
• Make sure each pile has a different number of bars in it.
• Use your calculator to see how much all the bars on the scale SHOULD weigh if all the bars are perfect.
• How many ounces too heavy is the fake bar?
• I bet you can finish it from here.