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一、凑整法 1、直接凑整。根据加法和乘法交换律、结合律,把能凑整的几个数,直接交换,结合起来速算。
First, rounding method 1, direct rounding. According to the law of addition and multiplicative exchange law, combined with the law, the number of rounding can be exchanged directly, combined with quick calculation.