APA (7th ed.) Citation

Townsend, C. B. (1990). World's toughest puzzles. Sterling Publishing.

Chicago Style (17th ed.) Citation

Townsend, Charles Barry. World's Toughest Puzzles. New York: Sterling Publishing, 1990.

MLA (9th ed.) Citation

Townsend, Charles Barry. World's Toughest Puzzles. Sterling Publishing, 1990.

Warning: These citations may not always be 100% accurate.