You have five pennies arranged on a square grid so that each one touches at least one other penny and they all form an "L" (above left).

Move the pennies one at a time to invert the "L" (above right), making sure that a penny always ends up in a new position on the grid where it touches at least two other pennies.

Can you do it? If so, how many moves does it take?

Try it below. Select the coin that you want to move by clicking on it. Its color will change to blue. Then click on the square to which you would like to move the selected coin. If it's an allowed move, the square will be colored green. If it's not allowed, the space will be red. Click "Reset" if you want to start again. Click "Undo" if you want to go back one move.

NOTE: To do this puzzle, you Web browser must be able to run Java applets.

Java applet created by Eric Peterson, 16, Washington, D.C.

Here's another coin-sliding challenge. Follow the same rules to rotate the "L" by 90° (as shown below). How many moves does it take?

Here's still another coin-sliding challenge. Change H into O or O into H. In this case, two coins that are next to each other diagonally are considered to be touching.

NOTE: The following applet runs best on Netscape, Firefox, Opera, and some versions of Internet Explorer.

Java applet created by Susan White, based on a program by Eric Peterson.

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