Fifty-seven to nothing
Lay out six matchsticks to form the Roman numeral LVII (fifty-seven). Now move exactly two of those six matches — leaving the other four untouched — so that what remains represents zero, or 'nothing' instead. Dudeney claimed there are two completely different ways to do it. Can you find one?
Reveal the answer
Two of Dudeney's solutions: move the two matches forming the 'L' to draw a square-root sign over the remaining 'VII', reading it as the square root of (I minus I), which is 0; or move those same two matches to spell 'NIL' instead of LVII. Dudeney originally posed it with six cigarettes rather than matches, in Modern Puzzles (1926), puzzle #216, later reprinted in 536 Puzzles and Curious Problems.