Clapp, F. L., & Huebner, B. P. (1924). The number combinations, their relative difficulty and the frequency of their appearance in text-books.
Citação norma ChicagoClapp, Frank L., and Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. Madison, Wis, 1924.
Citação norma MLAClapp, Frank L., and Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. 1924.
Nota: a formatação da citação pode não corresponder 100% ao definido pela respectiva norma.