Pillow-Problems by Charles L. Dodgson (Lewis Carroll)

The book Pillow-Problems by Charles L. Dodgson (who is better known by the pseudonym Lewis Carroll) contains 72 original mathematical puzzles. While Carroll had worked all of them out in his head and encouraged the reader to do the same, many of the puzzles are not particularly easy. The book's original subtitle was Thought Out During Sleepless Nights, but Carroll changed the subtitle to Thought Out During Wakeful Hours so that his friends didn't think that he suffered from insomnia.

The following problems are available on Math Lair: 1, 2, 3, 4, 5, 8, 10, 12, 13, 14, 15, 16, 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 38, 39, 40, 41, 44, 45, 47, 50, 52, 68, 70, 72.

For a list of problems sorted by topic, see Subjects Classified. Note that Dodgson refers to probability as "chances."

Sources used (see bibliography page for titles corresponding to numbers): 21, 22.