Problem Four: 16 Coins
Sep 28th, 2006 by Allen
Johnny was given 16 coins by his older, somewhat meaner brother, Mark. He told him that he could keep them all if he could place all 16 on the table in such a way that they formed 15 rows with 4 coins in each row.
After 10 minutes, Johnny walked away with the coins and Mark, after complaining futilely to his mother, left with nothing.
How did Johnny place the coins?
Update: Solutions are posted!
Johnny took the coins and ran.