Samuelson, P. A., & Samuelson, W. (1980). Economics (11th ed.). McGraw-Hill.

Samuelson, Paul Anthony, and William Samuelson. Economics. 11th ed. New York: McGraw-Hill, 1980.

Samuelson, Paul Anthony, and William Samuelson. Economics. 11th ed. McGraw-Hill, 1980.