Henry Ernest Dudeney/Modern Puzzles/5 - Doubling the Value

Modern Puzzles by Henry Ernest Dudeney: $5$

Doubling the Value

It is a curious fact that if you double $\pounds 6 \ 13 \shillings$, you get $\pounds 13 \ 6 \shillings$, which is merely changing the shillings and the pounds.

Can you find another sum of money that has the same peculiarity that, when multiplied by any number you may choose to select, will merely exchange the shillings and the pounds?

There is only one other multiplier and sum of money, besides the case shown, that will work.

What is it?

Sources

• 1926: Henry Ernest Dudeney: Modern Puzzles ... (previous) ... (next): Arithmetical and Algebraical Problems: Money Puzzles: $5$. -- Doubling the Value