QOD #18
Riki, Peter, Henry, Paul, and Stas, (e.g. the usual group that appears in all the QODs) were mulling around last night talking about information theory problems. After they were give an example problem with weighing balls, they thought they could figure out any problem the TA could think of.
"I," said Riki.
"Can," said Peter.
"Figure," said Paul.
"This," said Henry.
"Bug," said Stas.
"NOOOOOO!" said Peter. "It's 'OUT,' you idiot!"
"Very good, number one," said Paul.
* * *
Here's the problem.
You have 10 stacks of coins, each consisting of 10 half-dollars. One entire stack is counterfeit, but you do not know which one. You do know the weight of a genuine half-dollar and you are told that each counterfeit coin weighs one gram more than it should. You may weigh the coins on a pointer scale. What is the smallest number of weighings necessary to determine which stack is counterfeit?
Solution and comments
