五年级上册数学 小数简便运算13类常考题型 加法交换律 0.75+9.8+0.25 = 0.75+0.25+9.8 = 1+9.8 = 10.8 加法结合律 48.5+0.4+0.6 =48.5+(0.4+0.6) =48.5+1 =49.5 乘法交换律 2.5×5.6×0.4 = 2.5×0.4×5.6 = 1×5.6 = 5.6 乘法结合律 99×12.5×0.8 = 99×(12.5×0.8) = 99×10 = 990 加法交换律与结合律 6.5+0.28+3.5+0.72 =(6.5+3.5)+(0.28+0.72) =10+1 =11 乘法交换律与结合律 2.5×1.25×0.4×0.8 =(2.5×0.4)×(1.25×0.8 ) = 1×1 =1