Why is 6 + 7 equal to 13? For many adults, there has never been any real explanation for these answers; they just are. All you need to do is learn them. But today the goal is not to know the result, it is even more important to understand "how the result is arrived at."
三加五為何等於八，七加六為何等於十三，在如今許多成人學數學的經驗中，也許沒有理由可講，只要練習得熟，記得結果便是，但如今的數學的教學目標不只要知道結果，更重要的是知道「這結果是怎樣得出來的」。