Morton, R. L. (1937). Teaching arithmetic in elementary school. Silver Burdett company.
Lua i Stíl Chicago (17ú heag.)Morton, Robert Lee. Teaching Arithmetic in Elementary School. New York, boston [etc.]: Silver Burdett company, 1937.
Lua MLA (9ú heag.)Morton, Robert Lee. Teaching Arithmetic in Elementary School. Silver Burdett company, 1937.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.