My little gnome brain still hurts from trying this puzzle.
One hundred very smart garden gnomes are snatched from their homes by an evil wizard. He tells them he is going to line them all up in a row. They won’t be able to see the color of their own hats or anyone’s behind them, but they will be able to see the hats of the gnomes in front of them. The wizard will start at the back of the line and ask each gnome to guess the color of his own hat. Each gnome can only answer “red” or “blue”. If he gives the wrong answer, he will be led off to work on the wizard’s landscaping for the rest of eternity. If he answers correctly, he will be returned to his own garden.
From the wee folks at Make Magazine.