Henry Ernest Dudeney/Modern Puzzles/59 - The Two Digits

Modern Puzzles by Henry Ernest Dudeney: $59$

The Two Digits

Write down any $2$-figure number (different figures and no $0$)

and then express that number by writing the same figures in reverse order,

with or without arithmetical signs.

For example, $45 = 5 \times 9$ would be correct if only the $9$ had happened to be a $4$.

Or $81 = \paren {1 + 8}^2$ would do, except for the fact that it introduces a third figure: the $2$.

Sources

• 1926: Henry Ernest Dudeney: Modern Puzzles ... (previous) ... (next): Arithmetical and Algebraical Problems: Digital Puzzles: $59$. -- The Two Digits
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Arithmetical and Algebraical Problems: Digital Puzzles: $110$. The Two Digits