四则混合运算是小学数学的基础知识,也是各类竞赛中常考的内容。竞赛中的有关四则运算题综合性强、灵活性大,学生除了要具有扎实的基础外,还要掌握一定的速算与巧算的技巧,如凑整法、高斯求和法、裂项法、公式法、设元法等。下面就常用的方法与技巧举例加以说明。一、凑整法例1 Four mixed computing is the basic knowledge of elementary mathematics, but also a variety of competitions often test content. In the contest, the four arithmetic questions are comprehensive and flexible. Students should have some skills of calculating speed and calculating skills, such as rounding, Gaussian summation, split-law, Formula law, such as yuan law. The following commonly used methods and techniques to illustrate an example. First, rounding law 1