五上數(shù)學(xué)簡便計算?？?4類易錯題常用公式加法交換律：a+b=b+a加法結(jié)合律：(a+b)+c=a+(b+c)乘法交換律：a×b=b×a乘法結(jié)合律：(a×b)×c=a×(b×c)乘法分配律：(a+b)×c=a×c+b×c或(a-b)×c=a×c-b×c減法性質(zhì)：a-b-c=a-c-b或a-b-c=a-(b+c)除法性質(zhì)：a÷b÷c=a÷(b×c)或a÷b÷c=a÷c÷b去括號：a+(b-c)=a+b-ca-(b-c)=a-b+ca(b÷c)=ab÷aca÷(b÷c)=a÷b×c第一類：乘法結(jié)合律(1)3.29×0.25×4=3.29×(0.25×4)=3.29×1=3.29(3)0.25×8.5×4=(0.25×4)×8.5=1×8.5=8.5(2)0.35×1.25×2×0.8=(0.35×2)×(1.25×0.8)=0.7×1=0.7(4)0.8×(4.3×1.25)=0.8×1.25×4.3=1×4.3=4.3第二類：拆數(shù)+乘法結(jié)合律(1)0.125×8.8=0.125×8×1.1=1×1.1=1.1(2)0.25×0.28=0.25×4×0.07=1×0.07=0.07(3)0.125×3.2×2.5=0.125×(8×0.4)×2.5=(0.125×8)×(0.4×2.5)=1×1=1(4)0.25×36=0.25×4×9=1×9=9第三類：乘法分配律(1)3.5×99+3.5=3.5×(99+1)=3.5×100=350(2)3.5×9.9+3.5×0.1=3.5×(9.9+0.1)=3.5×10=35(3)7.6×0.8+0.2×7.6=7.6×(0.8+0.2)=7.6×1=7.6第四類：拆數(shù)+乘法分配律(1)35×10.2=35×(10+0.2)=35×10+35×0.2=350+7=357(2)2.8×103=2.8×(100+3)=2.8×100+2.8×3=280+8.4=288.4(3)0.85×199=0.85×(200-1)=0.85×200-0.85×1=170-0.85=169.15類型五：除法的性質(zhì)(1)7÷0.25÷4=7÷(0.25×4)=7÷1=7(2)7.35÷(7.35×0.25)=7.35÷7.35÷0.25=1÷0.25=4(3)15÷0.125÷8=15÷(0.125×8)=15÷1=15類型六：拆數(shù)+除法的性質(zhì)(1)4.9÷1.4=4.9÷(7×0.2)=4.9÷7÷0.2=0.7÷0.2=3.5(2)2.7÷4.5=2.7÷(9×0.5)=2.7÷9÷0.5=0.3÷0.5=0.6(3)4.5÷1.8=4.5÷(9×0.2)=4.5÷9÷0.2=0.5÷0.2=2.5類型七：積不變的規(guī)律+乘法分配律(1)3.5×2.7+35×0.73=3.5×2.7+3.5×7.3=3.5×(2.7+7.3)=3.5×10=35(2)32.4×0.9+10×0.324=32.4×0.9+0.1×32.4=32.4×(0.9+0.1)=32.4×1=32.4類型八：類似分配律“(a+b)÷c或(a-b)÷c”型(1)(32+5.6)÷0.8=32÷0.8+5.6÷0.8=40+7=47(3)3.5÷0.6-0.5÷0.6=(3.5-0.5)÷0.6=3÷0.6=5(2)(12.5-3.5)÷0.5=12.5÷0.5-3.5÷0.5=25-7=18(4)(7.7+4.2)÷0.7=7.7÷0.7+4.2÷0.7=11+6=17類型九：同級運算交換(1)0.25×4÷0.25×4=0.25÷0.25×4×4=1×4×4=16(2)7.5+2.5-7.5+2.5=7.5-7.5+2.5+2.5=0+2.5+2.5=5(3)3.29+0.73-2.29+2.27=3.29-2.29+0.73+2.27=1+0.73+2.27=1+3=4(4)3.25+1.79-0.59+1.75=3.25+1.75+1.79-0.59=5+1.79-0.59=6.79-0.59=6.2類型十：括號前為減號或除號,脫括號變符號(1)7.325-(5.325-1.7)=7.325-5.325+1.7=2+1.7=3.7(2)7.35÷(7.35÷0.25)=7.35÷7.35×0.25=1×0.25=0.2類型十一：加法結(jié)合律(1)3.29+0.73+2.27=3.29+(0.73+2.27)=3.29+3=6.29(2)7.25+3.58+2.25=(7.25+2.25)+3.58=10+3.58=13.58(3)5.34+4.23+6.77=5.34+(4.23+6.77)=5.34+11=16.34類型十二：減法交換(1)7.325-3.29-3.3=7.325-3.325-3.29=4-3.29=0.71(2)24.365-8.46-8.365=24.365-8.365-8.46=16-8.46=7.54類型十三：減法的性質(zhì)(1)7.325-(5.325+1.7)=7.325-5.325-1.7=2-1.7=0.3(2)3.29-0.73-2.27=3.29-(0.73+2.27)=3.29-3=0.29(3)3.07-0.38-1.62=3.07-(0.38+1.62)=3.07-2=1.07類型十四：減法交換+減法性質(zhì)(1)23.4-0.8-13.4-7.2=23.4-13.4-0.8-7.