5.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 6.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 7.乘法分配律(提取式) 1.35×12-1.35×2 = 1.35×(12-2) = 1.35×10 = 13.5 95.5÷1.6-15.5÷1.6 =(95.5-15.5)÷1.6 = 80÷1.6 = 50