Henry Ernest Dudeney/Modern Puzzles/18 - A Curious Paradox

Modern Puzzles by Henry Ernest Dudeney: $18$

A man went into a shop to pay a little bill that he owed.

On placing the money on the counter he found that he had not quite sufficient,

owing to a small purchase that he had thoughtlessly made on the way.

"I am so sorry," he said, "but you see I am a little short.

"Oh, that is all right," replied the tradesman, after looking at the money, "it won't make any difference to me."

"My good man!" exclaimed the customer ...

... etc. etc. ...

"... But really it will not affect my pocket in the slightest."

Can you explain the mystery?

It may come to you in a flash.

The tradesman was certainly correct.

1926: Henry Ernest Dudeney: Modern Puzzles ... (previous) ... (next): Arithmetical and Algebraical Problems: Money Puzzles: $18$. -- A Curious Paradox