Johnson, D. A. (1956). How to use field trips in mathematics. National Council of Teachers of Mathematics.
Lua i Stíl Chicago (17ú heag.)Johnson, Donovan A. How to Use Field Trips in Mathematics. Washington, D. C: National Council of Teachers of Mathematics, 1956.
Lua MLA (9ú heag.)Johnson, Donovan A. How to Use Field Trips in Mathematics. National Council of Teachers of Mathematics, 1956.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.