四年级下册数学小数加减法简便运算★在小数加减法计算中运用整数加法运算律和减法的性质，使其能够简便计算的关键在于凑十法，凑整法。加法交换律：a+b=b+a加法结合律：(a+b)+c=a+(b+c)整数减法的运算性质：①(a-b)-c=a-(b+c)②a-b-c=a-c-b加法结合律：5.3+(17.13-4.7)+0.870.57+13.36+1.43+6.64=5.3+17.13-4.7+0.87=(0.57+1.43)+(13.36+6.64)=(5.7-4.7)+(17.13+0.87)=2+20=18.6=2214.15-4.75+1.85-2.2514.7+5.9-14.7+5.9=14.15+1.85-4.75-2.25=(14.7-14.7)+(5.9+5.9)=(14.15+1.85)-(4.75+225)=0+11.8=9=11.8减法运算性质：58.92-15.5-18.92-4.518.917-(4.917+5.73)=(58.92-18.92)-(15.5+45)=18.917-4.917-5.73=40-20=14-5.73=20=8.271.29-3.7+9.71-6.380-12.4-7.6=1.29+9.71-(3.7+6.3)=80-(12.4+7.6)=11-10=80-20=1=602.8×101-2.80.25×4.4300-2730÷91-70=2.8×(101-1)=0.25×4+0.25×0.4=300-30-70=2.8×100=1+0.1=300-(30+70)=280=1.1=200125×48568-(68+178)6.78+2.04+7.22+5.96=125×8×6=568-68-178=(6.78+7.22)+(2.04+5.96)=1000×6=500-178=14+8=6000=322=22400-(1300÷65+35)6.45-(2.31-1.55)8.49+(4.64-2.14)×0.64=400-(20+35)=6.45-2.31+1.55=8.49+2.5×0.64=400-55=6.45+1.55-2.31=8.49+2.5×4×0.16=345=5.69=10.0964×39+37×39-3923.4-8.54-1.46101×78-78=39×(64+37-1)=23.4-(8.54+1.46)=(101-1)×78=39×100=23.4-10=100×78=3900=13.4=78002.88+2.3+4.71050÷15÷74.2×99+4.2=2.88+(2.3+4.7)=1050÷(15×7)=4.2×(99+1)=2.88+7=1050÷105=4.2×100=9.88=10=420103×87-93×876.92-(3.2+1.92)5.02-3.5+0.98=(103-93)×87=6.92-1.92-3.2=(5.02+0.98)-3.5=10×87=5-3.2=6-3.5=870=1.8=2.525.86+7.8-5.863.2+6.8×1.25×816.8÷0.5÷2=25.86-5.86+7.8×8)=3.2+6.8×1.25×8=16.8÷(0.5×2)=20+7.8=3.2+6.8×10=16.8÷1=27.8=71.2=16.83.27+5.49-1.27+4.510.8×3.37×12.510-2.8-7.2=3.27-1.27+(5.49+4.51)=(0.8×12.5)×3.37=10-(2.8+7.2)=2+10=10×3.37=10-10=12=33.7=07.5-7.5×0.92.5×444.8×102=7.5×1-7.5×0.9=2.5×4×11=4.8×(100+2)=7.5×(1-0.9)=10×11=4.8×100+4.8×2=0.75=110=489.69.16×1.53-0.053×91.64.5+4.5×998.08×1.25=9.16×1.53-0.53×9.16=4.5×1+4.5×99=1.01×(8×1.25)=9.16×(1.53-0.53)=4.5×(1+99)=1.01×10=9.16=450=10.16.74+12.62+24.38+3.263.7×0.25×49.75-(6.75+0.4)=(6.74+3.26)+(12.62+24.38)=3.7×(0.25×4)=9.75-6.75-0.4=10+37=3.7×1=3-0.4=47=3.7=2.66.78+2.04+7.22+5.962.6×992.43×45+24.3×5.5=(6.78+7.22)+(2.04+5.96)=2.6×(100-1)=2.43×45+2.43×55=14+8=2.6×100-2.6×1=2.43×(45+55)=22=257.4=2430.25×4.42.8×101-2.81.29-3.7+9.71-6.3=0.25×4+0.25×0.4=2.8×(101-1)=1.29+9.71-(3.7+6.3)=1+0.1=2.8×100=11-10=1.1=280=16.45-(2.31-1.55)23.4-8.54-1.466.92-(3.2+1.92)=6.45-2.31+1.55=23.4-(8.54+1.46)=6.92-1.92-3.2=6.45+1.55-2.31=23.4-10=5-3.2=5.69=13.4=1.85.02-3.5+0.9825×1.25×3225.86+7.8-5.86=(5.02+0.98)-3.5=25×1.25×4×8=25.86-5.86+7.8=6-3.5=(25×4)×(1.25×8)=20+7.8=2.5=1000=27.80.8×3.37×12.54.2×99+4.24.25÷2.5×101-1.7=(0.8×12.5)×3.37=4.2×(99+1)=1.7×101-1.7=10×3.37=4.2×100=1.7×(101-1)=33.7=420=170103×4.55.6×0.8×12.50.56×101-0.56=(100+3)×4.5=5.6×(0.8×12.5)=0.56×(101-1)=100×4.5+3×4.5=5.6×10=0.56×100=465.3=56=56(2.56-1.18)÷2.3×1.54×9.04×2.580-12.4-7.6=1.38÷2.3×1.5=9.04×(4×2.5)=80-(12.4+7.6)=0.6×1.5=9.04×10=80-20=0.9=90.4=60