APA (7th ed.) Citation

Ruffin, R. J., & Gregory, P. R. (1990). Principles of economics (4th ed.). Scott, Foresman.

Chicago Style (17th ed.) Citation

Ruffin, Roy J., and Paul R. Gregory. Principles of Economics. 4th ed. Glenview, Illinos: Scott, Foresman, 1990.

MLA (9th ed.) Citation

Ruffin, Roy J., and Paul R. Gregory. Principles of Economics. 4th ed. Scott, Foresman, 1990.