My dad, 72, had me create this penny puzzle. I used solidworks to figure out the exact size the square needed to be to fit all 10 in a certain configuration. It
Ten Penny Puzzle - Frames Games & Things Unnamed
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10 Penny Puzzle
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10 Penny Puzzle - a circle packing problem - YouTube
Amazon.com: 10 Penny Puzzle - A Circle Packing Problem - Ten Mint Pennies are Included : Toys & Games