Collating the Coins

after Martin Gardner

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Millennium Puzzles - Puzzles.COM SelectArrange five coins (three bigger and two smaller ones) as shown above (top row). 

The problem is to change their positions to those shown at the bottom of the illustration in the shortest possible number of moves.

A move consists of placing the tips of the first and second fingers on any two touching coins, always of the different sizes, then sliding the pair to another spot along the imaginary line shown in the illustration. The two coins in the pair must touch at all times. The coin at left in the pair must remain at left; the coin at right must remain at right. Gaps in the chain are allowed at the end of any move except the final one. After the last move the coins need not necessarily be at the same spot on the imaginary line that they occupied at the start.

Updated: June 16, 2011  |   Posted: June 21, 2004
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