Heddens, J., Speer, W. Today's Mathematics. New York: Macmillan Publishing Company, 1988 677 с. 0-02-352931-8.
Heddens, J., Speer, W. Today's Mathematics. New York: Macmillan Publishing Company, 1988 677 с. 0-02-352931-8.
Heddens, J., Speer, W. (1988) Today's Mathematics, New York: Macmillan Publishing Company 677 с. 0-02-352931-8.
Heddens, J., & Speer, W. (1988). Today's Mathematics. Consepts and Methods in Elementary School Mathematics. New York: Macmillan Publishing Company, 677 с.
Heddens J, Speer W. Today's Mathematics: Consepts and Methods in Elementary School Mathematics. New York: Macmillan Publishing Company; 1988. p. 677 с. ISBN: 0-02-352931-8.
