20 puzzles from Henry Dudeney, each explained in a minute and credited to the original work. Free on Savvy.
Cut an equilateral triangle into as few pieces as possible so they can be rearranged into a perfect square. Henry Dudeney's solution goes further than the challenge asks — his four…
— Henry Dudeney, The Canterbury Puzzles
In a rectangular room 30 feet long, 12 feet wide and 12 feet high, a spider sits on one end wall, a foot below the ceiling and centred. A fly sits on the opposite wall, a foot abov…
— Henry Ernest Dudeney, The Canterbury Puzzles
SEND + MORE = MONEY. Each letter represents a different digit 0–9 (no leading zeros), and the addition has to work exactly as written. Find the digits.
— Henry Dudeney, The Strand Magazine, Vol. 68
Three houses each need a line running to three separate utility companies — water, gas and electricity. Can you draw all nine connecting lines on a flat sheet of paper so that no t…
— Henry Dudeney, Amusements in Mathematics
Two black frogs and two white frogs sit on a strip of seven lily pads, black on the left, white on the right, one empty pad in the middle. Moving one frog at a time — sliding onto …
— Henry Ernest Dudeney, Amusements in Mathematics
Write the digits 1 through 9 in ascending order, then insert plus and minus signs between some of them (digits may be pushed together to form bigger numbers, but never reordered or…
— Henry Ernest Dudeney, Amusements in Mathematics
A retired professor claims to have found a magic shortcut for cube roots: just add up a number's digits, and that sum is its cube root. Test it on 512 — its digits sum to 8, and 8 …
— Henry Dudeney, 536 Puzzles and Curious Problems
For Christmas, Mrs. Perkins receives a patchwork quilt made of 169 small squares of silk, all sewn into one large 13-by-13 square. She decides to unpick it and re-cut it into the s…
— Henry Ernest Dudeney, Amusements in Mathematics
A milkmaid starts at a stool, must walk to a straight stream to fill her pail, then carry it to a barn door. The stream doesn't lie directly between them — it's off to one side. Sh…
— Henry Dudeney, Amusements in Mathematics
A Greek cross — five equal squares arranged in a plus shape — sits on your table. Using only four straight cuts, can you slice it into pieces that reassemble, edge to edge with no …
— Henry Dudeney (ed. Martin Gardner), 536 Puzzles and Curious Problems
In one of Henry Dudeney's puzzles, a retired professor claims to have found a trick for extracting cube roots: add up a number's digits, cube that total, and you land back on the n…
— Henry Dudeney, Modern Puzzles
I paid a shilling for some apples, but they were so small the seller threw in two extra for the same money. That worked out to exactly a penny a dozen less than the price he'd firs…
— Henry Ernest Dudeney, Amusements in Mathematics
Henry Dudeney set this chessboard challenge in 1900: place as many pawns as possible on an 8x8 board so that no three of them ever fall on a single straight line — at any angle, no…
— Henry Dudeney, No-three-in-line problem
Arrange six pennies in a triangle: three along the bottom, two above them, one on top, each coin touching its neighbours. Now move the coins one at a time into a straight line of s…
— Henry E. Dudeney, 536 Puzzles and Curious Problems
Henry Dudeney's landowner has a square plantation of 49 trees planted in neat rows and columns. A storm blows down 4 of them. He decides to fell all but ten of the trees left stand…
— Henry Dudeney, Amusements in Mathematics
A merchant has six sealed barrels holding 15, 16, 18, 19, 20 and 31 gallons. Five contain wine, one contains beer, but none are labelled. He sells one buyer some wine, and a second…
— Henry Ernest Dudeney, Amusements in Mathematics
Three round buns, all the same size and thickness, need to be divided into shares so that four boys receive exactly equal amounts. Cuts can be made anywhere, but the puzzle asks fo…
— Henry Dudeney, Amusements in Mathematics
Using the same seven tangram pieces arranged two different ways, you can build two monk figures that look almost identical — except one of them is clearly missing a foot. Both figu…
— Henry Dudeney, Amusements in Mathematics
Take a strip of eight postage stamps in a row, each joined to the next by a perforation. Using only the existing creases, fold the strip into a single stack the size of one stamp. …
— Henry Dudeney, Modern Puzzles and How to Solve Them
Set up a row of bowling pins. Two players take turns: on each turn, knock down either a single pin, or two pins that happen to be standing right next to each other. Whoever knocks …
— Henry Ernest Dudeney, The Canterbury Puzzles