APA (7e ed.) Bronvermelding

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

Chicago (17e ed.) Bronvermelding

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

MLA (8e ed.) Bronvermelding

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