Henry Ernest Dudeney/Puzzles and Curious Problems/250 - Adjusting the Counters

Puzzles and Curious Problems by Henry Ernest Dudeney: $250$

Adjusting the Counters

Place $25$ counters in a square in the order shown.

Then it is a good puzzle to put them all into regular order so that the first line reads $1 \ 2 \ 3 \ 4 \ 5$, and the second $6 \ 7 \ 8 \ 9 \ 10$,

and so on to the end, by taking up one counter in each hand and making them change places.

The puzzle is to determine the fewest possible exchanges in which this can be done.

Sources

• 1932: Henry Ernest Dudeney: Puzzles and Curious Problems ... (previous) ... (next): Moving Counter Problems: $250$. -- Adjusting the Counters
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Geometrical Problems: Moving Counter Puzzles: $375$. Adjusting the Counters