太神了! 日本小學生是這樣做乘法的！ 


13×12是多少？除了使出小算盤以外，你也可以...
不過考試好像會浪費很多時間...


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Color the edges and diagonals of a regular polygon

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Relationship between determinant of matrix and determinant of adjoint?

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What is the equation of a 3D cone with generalised tilt?

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