Cita APA (7a ed.)

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

Cita Chicago Style (17a ed.)

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

Cita MLA (9a ed.)

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