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A teacher showing a math problem on the blackboard in front of the class.
Keywordsteacher, math, students, blackboard, chalkboard
George Wentworth and David Eugene Smith School Arithmetics: Primary Book (Boston: Ginn and Company, 1919) 52
2400×1718, 2.5 MiB
1024×733, 347.9 KiB
640×458, 162.6 KiB
320×229, 46.1 KiB