Freund, J. E., & Williams, F. J. a. (1964). Elementary business statistics: The modern approach. Prentice - hall.

Freund, John E., and Frank J.[et al] Williams. Elementary Business Statistics: The Modern Approach. New Jersey: Prentice - hall, 1964.

Freund, John E., and Frank J.[et al] Williams. Elementary Business Statistics: The Modern Approach. Prentice - hall, 1964.