Cita APA (7a ed.)

Clapp, F. L., & Huebner, B. P. (1924). The number combinations, their relative difficulty and the frequency of their appearance in text-books.

Cita Chicago Style (17a ed.)

Clapp, Frank L., y Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. Madison, Wis, 1924.

Cita MLA (8a ed.)

Clapp, Frank L., y Bernard P. Huebner. The Number Combinations, Their Relative Difficulty and the Frequency of Their Appearance in Text-books. 1924.