b×ca×b×c=a×(b×c)乘法结合律乘法交换律乘法分配律一、用简便方法计算①46+32+54②0.7+3.9+4.3+6.1=(46+54)+32=100+32=132=(0.7+4.3)+(3.9+6.1)=5+10=15运用加法交换律和加法结合律③25×49×4④8×4×12.5×0.25=(8×12.5)×(4×0.25)=100×1=100=25×4×49=100×49=4900运用乘法交换律和结合律①(25+8)×4②0.25×25+0.75×25③15×102④59×99⑤907×99+907⑥0.5×9+0.5⑦7/9×5/6+7/9÷6⑧2÷9/7+8÷9/7⑨6.3×2.57+25.7×0.37二、你能用最简便的方法计算吗?1、普通型①(25+8)×4②0.25×25+0.75×25=25×4+8×4=100+32=132=(0.25+0.75)×25=1×25=25①15×102②59×992、拆分型=15×(100+2)=15×100+15×2=1500+30=1530=59×(100-1)=59×100-59×1=5900-59=5841①907×99+907②0.5×9+0.5=907×99+907×1=907×(99+1)=907×100=90700=0.5×9+0.5×1=0.5×(9+1)=0.5×10=53、缺项型(运用1的性质)4、积不变规律(小数点的移动)①6.3×2.57+25.7×0.37=6.3×2.57+(25.7÷10)×(0.37×10)=6.3×2.57+2.57×3.7=2.57×(6.3+3.7)=2.57×10=25.7①6.3×2.57+25.7×0.37=(6.3÷10)×(2.57×10)+25.7×0.37=0.63×25.7+25.7×0.37=25.7×(0.63+0.37)=25.7×1=25.7
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