Johnson, D. A. (1956). How to use field trips in mathematics. National Council of Teachers of Mathematics.
Chicago-viite (17. p.)Johnson, Donovan A. How to Use Field Trips in Mathematics. Washington, D. C: National Council of Teachers of Mathematics, 1956.
MLA-viite (9. p.)Johnson, Donovan A. How to Use Field Trips in Mathematics. National Council of Teachers of Mathematics, 1956.
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