Day, R. A., & Underwood, A. L. 1. (1991). Quantitative analysis (6th ed.). Prentice Hall Intenational.
Dyfyniad Arddull ChicagoDay, Reuben Alexander, and Arthur Louis 1924 Underwood. Quantitative Analysis. 6th ed. Englewooe Cliffs, NJ: Prentice Hall Intenational, 1991.
Dyfyniad MLADay, Reuben Alexander, and Arthur Louis 1924 Underwood. Quantitative Analysis. 6th ed. Prentice Hall Intenational, 1991.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.