APA (7th ed.) Citation

Langum, J. K., Garver, F. B., & Hansen, A. H. (1939). Problems and questions on the Principles of economics. Ginn and company.

Chicago Style (17th ed.) Citation

Langum, John K., Frederic Benjamin Garver, and Alvin H. Hansen. Problems and Questions on the Principles of Economics. Boston, New York [etc.]: Ginn and company, 1939.

MLA (9th ed.) Citation

Langum, John K., et al. Problems and Questions on the Principles of Economics. Ginn and company, 1939.