mathematical addition and subtraction artifact double-sided less than 20 addition and subtraction teaching aids 10 digital decomposition ruler first grade learning calculation 数学加减法神器双面20以内加减法教具10数字分解尺一年级学习计算

(double-sided available side 20 side 10) blue 1 (double-sided available one side 20 one side 10) pink 1 (available on both sides) pink 1+1 blue (two sides can be used one side 20 one side 10) blue 2 (two sides can be used one side 20 one side 10) pink 2 [activity angle] blue 1 [activity angle] pink 1

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