Remove five pennies, add four, and somehow nine are left. How?
A guest lays eleven pennies on the table and makes a claim: 'Remove five of these coins, then add four more, and you will leave nine.' Everyone assumes ten pennies must remain on the table. They're wrong — what's going on?
Reveal the answer
The nine isn't left on the table — it's left in the pile of coins you removed. Take away five pennies, then add four more pennies to that same removed pile, and the pile you set aside now holds nine. The eleven on the table were never the subject of the sentence at all.
— Henry Dudeney, The Canterbury Puzzles — Puzzle 56, 1907
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