北师大四年级数学下册小数乘法简便计算

#年级下册小数练习题7.8x1.3+0.948-1.8x240.25x0.46x0.42.5x1.3+0.93.8x41-3.8(4+0.4)x2.50.27x3.8+0.27x6.22.9x100.127.5x101-27.540x0.63x0.253.62x25.7+3.62x74.30.25x4.87x4一、脱式计算，能简算的要简算。18.8+23.6+26.410.95-3.74-4.2695.59-(9.59+12.78)25.6-(0.23+5.6)-1.7713.75-(4.75+6.48)7.83+2.34-0.83+6.663.82+2.9+0.18+9.15.93+0.19+2.8125.48-((9.4-0.52)3.07-0.38-1.6235.6-1.8-15.6-7.27.3+2.7-7.3+2.748.4+2.78+51.6-0.7823.4+0.8-13.4-7.24.8+8.63+5.2+0.373.25+2.76+1.751.27+3.9+0.73+15.15.84-1.8-3.2132.44-(58.74+19.44)7.5+4.8-6.57.14-0.53-2.4713.75-(3.75+6.48)13.45-4.68+2.557.14-0.53-2.4713.75-(3.75+6.48)13.45-4.68+2.5547.8-7.45+8.236.8-4.5+6.9849.8-9.6+8.815.2-6.8-3.4576+0.65+3.2436.8-4.5+6.9849.8-9.6+8.815.2-6.8-3.4576+0.65+3.240.134+2.66+0.87.5+4.9-6.33.45+1.79+0.654.85+8.63+0.371.76+3.44+0.3536.54-1.76-8.668-2.45-1.0223.4+3.4-0.236.02+3.6+1.983.07-0.38-1.627.5+4.9-6.536.8-3.9-6.883.285+1.79+0.5923.4-0.8+13.432+4.9-8.61.29+3.7+2.715.93+0.49+2.069-2.45-1.6521+0.56+11.364.89-7.88-13.60.134+2.66+0.87.5+4.9-6.33.45+1.79+0.654.85+8.63+0.371.76+3.44+0.3536.54-1.76-8.668-2.45-1.0223.4+3.4-0.236.02+3.6+1.983.07-0.38-1.627.5+4.9-6.536.8-3.9-6.883.285+1.79+0.5923.4-0.8+13.432+4.9-8.61.29+3.7+2.715.93+0.49+2.069-2.45-1.6521+0.56+11.364.89-7.88-13.6二、能简便的要简便计算。125x8.2x80L23x1.4+a23x8L6125x8.2x80L23x1.4+a23x8L60.125((80+0.8)0.4x0.16x2.556x1017.85x99115x99+115162x101-16245x0.78+5.5x7.88+7.2x0.810.34x2.5x0.41.25x11x4x0.88.93x5.7+8.93x3.3+8.9356x1017.85x99115x99+115162x101-16245x0.78+5.5x7.88+7.2x0.810.34x2.5x0.41.25x11x4x0.88.93x5.7+8.93x3.3+8.934.82x1020.7x0.46+0.7x0.545.6-4.34+7.34685.7-(15.3-4.8)25.4-(15.3+7.7)3.6－1.28+3.093.8-0.46-1.72325.6-(0.23+5.6)-1.7713.75-(4.75+6.48)0.83+6.663.82+2.9+0.18+9.125.48-((9.4-0.52)35.6-1.8-15.6-7.25.93+0.19+2.817.3+2.7-7.3+2.73+5.2+0.373.07-0.38-1.627.83+2.34-48.4+2.78+51.6-0.7823.4+0.8-13.4-7.24.8+8.61.27+3.9+0.73+15.15.84-1.8-3.2132.44-(58.74+19.44)6.513.45-4.68+2.5525+2.76+1.7513.75-(3.75+6.48)7.14-0.53-2.4747.8-7.45+8.236.8-4.5+6.9849.8-9.6+8.87.5+4.8-15.2-6.8-3.453.45+1.79+0.653.45+1.79+0.651.76+0.65+3.240.134+2.66+0.87.5+4.9-6.34.85+8.63+0.371.76+3.44+0.3536.54-1.76-8.663.45+1.79+0.657.5+4.9-6.523.4+3.4-0.236.02+3.6+1.983.07-0.38-1.6236.8-3.9-6.883.285+1.79+0.5923.4-0.8+13.49-2.45-1.29+3.7+2.7121+0.56+11.332+4.9-8.65.93+0.49+2.061.659-2.45-一、乘法交换律

axbxc=axcxb0・25x8・5x412・5x0.96x0・80.25x0.73x40.25x16・2x4二乘法结合律(axb)xc二ax(cxb)4・36x12・5x80・95x0・25x435x0・2x0・50・75x50x0・4三、乘法分配律(a土b)xc=axc土bxc125+2・5)x0・8(1・25－0・125)x8(20－4)125+2・5)x0・8axaxb土axc二a(b土c)3・72x33・72x3・5＋6・28x3・57・09x10・8－0・8x7・0910・6x0・35－9・6x0・3515・6x2・1－15・6x1・127・5x3・7－7・5x3・77・6x0・8＋0・2x7・63・83x4・56＋3・83x5・443・9x2・7＋3・9x7・30・8x100・10・79x990・85x1993・65x10・14・6x0・90・65x1014・8x10・13・6x1020・39x1998・9x1・010・32x4033・65x10・10・85x9・90・65x101六、拆分因数1・25x2・5x323・2x0・25x12・50・25x3625x4・48・8x1・25五、把其中一个因数分成两个数的和或差，再按乘法分配律七、添加因56・5x99＋56・59・7x99＋9・74・2x99＋4・25・4x11-5・41・87x9・9+0.18712・7x9・9+1.27八、更改因数的小数点位置6・66x3・3+66・6x6746x57＋23x864・8x7・8＋78x0・523・14x0・68＋31・4x0・032101x0・87-0・91x873・65x4・7－36・5x0・372・3x16+2・3x23+2・3314x0・043＋3・14x7・2－31・4x0・155x1・03x0・232x1・250・45x9953x10・10・125x9612・5x10・825x7・3x0・445x21－50x2・145x1・58＋5・5x15・84・2x6・51＋3・49x4・29・99x2・22＋3・33x3・343・8x2=10x0・7=13・9x0=5・5x1=1・8x0・5=3・2x3=0・08x1・25=2・5x4=2・5x8=0・6x0・1=0・7x0・8=2・5x8x0=3・8x2=10x0・7=13・9x0=三、直接写得数5・5x1=1・8x0・5=3・2x3=50・8x100=13・1x0・3=0・5x0・2=125x0・8=508400=13・1x0・3=0・08x1・25=0・6x0・1=、竖式计算2・8x0・7=7・05x2・4=2・5x4=0・7x0・8=13x0・15=0・46x7・9=2・5x8=2・5x8x0=0・39x0・6=89・3x7・6=0・5x0・2=125x0・8=0・38x600=60・5x400=3.05X18=4.6X18.9=40.5X4.2=0.37X2.31=3.8x0.12=0.57x0.6=6.4x0.5=6.7x5.8=9.8x3.8=7.8x64=4.6x2.7=4.5x2.7=5x1.6=3x0.6=3x1.2=6.7x7.6=54x7.8=2.6x3.6=3.5x1.7=8.3x2.6=14x0.7=4.5x2.8=7.4x2.6=6.2x1.4=5.4x2.6=2.3x1.4=3.7x1.8=4.5x2.3=5.2x1.6=3.6x0.8=0.66x1.4=6.5x5.8=0.72x0.49=0.42x0.28=0.24x0.19=2.4x1.3=0.72x0.27=0.78x0.32=0.65x0.04=0.23x0.16=0.29x0.15=0.16x0.19=4x1.2=7x4.6=6x0.37=0.28x0.27=0.75x0.42=2.3x1.9=8x0.64=2.7x0.8=10x4.2=7.1x3.9=4.3x1.4=2.6x1.6=0.8x0.3=0.65x0.4=0.91x0.6=1.8x1.6=4.8x0.5=3.2x0.4=9.8x4.8=12x8.3=15.2x6.5=20.1x11.1=13.34x10.32=6.52x0.48=6.3x5.1=8.7x3.6=14.3x4.3=1.5x0.54=10x4.2=2.47x3.24=2.98x0.56=5.64x1.78=8.02x0.98=7.1x3.9=2.8x11.39=12.53x4.67=7.2x6.45=1.65x3.35=7.96x1.45=60x1.27=6.07x4.89=5x0.41=0.9x0.5=2x0.7=1.2x4.3=5.4x2.7=6x2.9=3.7x1.7=4.2x0.8=7.5x2.5=

22x43=9.5x7.1=3.5x1.6=5.2x28=7.8x1.6=9.6x4.1=10x4.2=5.1x2.5=4.1x3.4=1.2x3.8=9.6x4.1=7.8x1.6=3.5x1.6=4.4x1.4=2.9x2.1=3,5x12=4.8x3.4=6.9x2.5=2.5x7.8=8x5.4=6.9x2.5=2x3.5=6.8x2.2=4.7x5.4=4.1x8.8=2.2x5.5=9.6x2.1=1.7x3.8=7.4x3.6=0.8x0.23=1.6x2.4=4.7x3.5=1.2x3.6=1.5x3.8=2.8x1.2=7.3x2.7=7.3x2.7=6.2x3.7=4.2x3.9=0.54x0.65=7.5x5.2=0.7x0.5=0.32x0.47=8.3x6.3=7.2x0.42=0.48x0.52=0.8x0.25=43.5x0.65=0.32x0.16=0.35x0.55=0.87x0.8=0.24x0.08=0.92x0.37=1.4x0.6=3.6x4.2=0.72x0.48=6.8x3.2=7.1x3.4=0.42x0.66=0.32x0.68=2.8x7.2=0.65x0.19=3.09x1.2=3.25x5.64=0.25x0.47=0.82x0.18=7.8x2.4=0.45x0.18=0.4x0.16=8.2x1.8=0.73x0.27=8x3.2=9.8x4.8=3x2.4=2.8x0.9=1.29x0.18=5.1x0.8=10x0.3=8.9x4.9=6.8x0.7=8x0.72=6.6x3.4=6.4x1.3=1.2x0.8=7.3x6.2=8.7x3.6=12.3x0.7=0.8x9.2=4.7x1.9=5.1x3.9=1.4x0.6=

3.8x64=0.6x7.45=4.9x0.1=4.5x3.2=1.8x0.9=6.5x0.5=10.5x6.5=7.5x0.5=0.78x0.28=12.8x2.8=9.6x2.3=3.8x0.12=0.8x0.08=10x7.4=7.5x3.2=0.42x0.58=0.8x0.15=2.5x0.4=8.2x2.6=1.4x0.7=2.5x4.6=0.5x9.8=6.7x2.6=7.2x5.9=8.7x3.6=5.69x2.48=2.9x4.1=9.1x6.7=2.03x1.2=8.6x4.9=1.3x2.03=9.46x7.21=1.56x2.24=3.5x1.25=0.75x0.4=20x0.78=4.8x4.2=5.7x3=4.9x1.7=1.34x0.8=2x0.75=8.7x0.03=0.2x0.09=8.5x2.5=3.4x1.4=0.68x0.42=7.82x7.2=2x9.1=0.48x0.52=8.1x5.1=0.78x0.24=0.8x0.18=0.89x0.25=1x0.98=0.9x0.1=1x0.8=4.5x4=5.6x4=5.7x3.3=10x4.4=6x6.6=9.5x2.7=1x0.55=五、列式计算。1、甲数是15.24，比乙数多7.6，乙数是多少？2、3．58加上7.08与5.1的差，和是多少？六、解决问题。1、小红用20元钱买文具，买钢笔用去6.7元，买文具盒用去9.8元，还剩下多少钱？2、爸爸用两条长度分别是1.27米、1.35米的绳子接起来捆扎报纸。接口处共用去绳子0.25米，接好后的绳子有多长？

3、一桶油连桶共重12.65千克，用去一半后，连桶还重6.85千克，原来的桶里有油多少千克？二、减法中的巧算1•减法的性质：a-b-c=a-(b+c)巧算下面各题：①30073-27②7.42-(3.42!5)③4723(72辭189)三、加减混合式的巧算1.去括号和添括号的法则在只有加减运算的算式里，如果括号前面是“＋”号，则不论去掉括号或添上括括号，号里面的运算符号都不变；如果括号前面是“-”号，则不论去掉括号或添上括号，括号里面的运算符号都要改变，“+”变“-”，“-”变“+”，即：a+(b+c+d)=a+b+c+da-(b+a+d)=a-b-c-da-(b-c)=a-b+c2带符号“搬家”325+46-125+54=325-125+46+54=(325-125)+(46+54)=200+100=300注意：每个数前面的运算符号是这个数的符号.如+46，-125，+54.而325前面虽然没有符号，应看作是+325。找“基准数”法几个比较接近于某一整数的数相加时，选这个整数为“基准数”。计算78+7+83+82+7+80+79+85二用简便方法计算：588+264+1488996+3458+75464995-(995-480)588+264+1488996+3458+75464995-(995-480)4250-294+94478-128+122-72464-54+599+345947+(372-447)-572537-(543-163)-57小数乘法的简便运算一、乘法交换律与结合律的运用。提示1：以下计算中，有的需要把一个小数拆成两个数相乘，要注意拆分后两数

相乘的大小应该与原数相等，特别是小傲的位数。如3.2=18x43.2=0L4x8OL32=L04x80.32=(108x45.6=018x75.6=017x80.56=0.07x80.56=0.08x70.48=0.12x40.48=0.04x12提示2：提示2：连乘用结合提示3:应用乘法结合律解题的格式是axbxc=ax(bxc)最后一个步骤是"x”,

不要看成是“+”.如2.5x0.48=2.5x0.04x12=0.1x12=1.24.56x0.4x2.512.5x2.7x0.812.5x3.2x0.252.5x0.4812.5x5.625x0.36乘法分配律的运用。提示1：A组中的一个因数都具备一个特点，都接近整数1、10、100等，这样的就可以拆分成两个数相加或者相减。就可以拆分成两个数相加或者相减。如10.4=(10+0.4)9.9=(10-0.9)0.99=(10-0.01)但也有这样的数8.8=(8+0.8)4.4=(4+0.4)0.48=(0.4+0.08)

提示2:应用乘法分配律解题的口诀是乘加乘减用分配提示3:应用乘法分配律解题的格式是(a+b)xc二axc+bxc最后一个步骤是"+',不要看成是x”.如2.5x0.48=2.5x(0.4+0.08)=2.5x0.4+2.5x0.08=1+0.2=1.2不是=1+0.2=2提示4：应用乘法分配律解题的最后一步，有时是数字比较大的两个数相加减，口算容易出错，这时就要打草稿竖式计算0.25x10.412.5x8.89.9x0.353.7x1.8－2.7x1.895.7x0.28＋6.3x0.28－0.28x21.08x9＋1.08

比较乘法结合律与分配律在简便运算时的区别。下面各题用两种方法简算125x8.8125x8.8125x8.8125x8.80.25x480.25x48二变一变，能简算表面上看来，左右两边没有相同的因数，48x0.56+44X0.48不能使用乘法分配律。我来试一试：0.279x343＋0.657x2790.264x519＋264x0.4819.16x1.53－0.053x91.6三、拓展提高。99.99x0.8＋11.11x2.8314x0.043＋3.14x7.2－31.4x0.15小数除法的简便运算小数除法的简便计算与整数除法的简便计算一样，用到的是除法性质。除法性质1、AvB-C=A-(BxC)如：4零28=42r(Q7x4)=42vQ7-4=60v4=15如：420-2.5-4=420-(2.5x4)=420-10=42除法性质2、(a－b)vc=avc－bvc除法性质3、Av(BvC)=AvBxC除法性质4、Ax(BvC)=AxBvC乘除法的递等式计算方法与整数的一样，能简便的要简便，但也有的是不能简便比如：3.6+6.4x0.5不能掉进先加后乘的陷阱里。3.6x5+15x6.4不能掉进应用乘法分配率的陷阱里。

73.8－1.64－13.8－5.3666.86－8.66－1.340L25x162x43.72x3.5+^28^3.536L8-3.9-6.125L48－(9L4－0L52)48x7.8+78x0.523.6x10264x0L25+3.6"32+4.9－0.94.8－4.8x0.5(1.25－0.125)x88x100.156.5x9.9+56.57.09x10.8－0.8x7.0902+5.4+0.985.17－1.8－3.213.75－(3.75+6.48)3.68+7.56－2.687.85+2.34－0.85+4.6635.6－1.8－15.6－7.23.82+2.9+0.18+9.19.6+4.8－3.67.14－0.53－2.4727+2.86－0.66+1.6313.35－4.68+2.6547.8－7.45+8.80.398+0.36+3.6415.75+3.59－0.59+14.2542.5－(6.07+1.13)42753201.2央818.76x9.9+18.763.52r2.5v0L44.78t0L2+3.443.9－4.1+6.1－5.90L49t1.41.25x2.5x323L6－0L6x23L65x10L13L6－3L6x0L815L2v0L25r45.6子3.59L6v0L8vOL442x99+420.89x100.11465-(23+465)17.8^(1.78x4)5.83x2+4.27(459-327)今8子0.1259.7x99+9.74.36x12.5x815.6x13.1－15.6－15.6x2.1O.65x1O127.5x3.7-7.5x3.78L54t2.5v0L43.83x456+3.83x5.446048+975-3045498x396048+75-3005648x75-30056098+935-1045404x24-7581048+975-345640x75今35878x2968x975-3459948+275-3045690x6子3568+975-34568+975子345648+75-35685+975-34568+975-345548x975-304548x975-3046748+975-50456048+975-30450.425<0,38^0,012Q》L074&35<5.57482Q》L074&35<5.5748＋95-4548x975-30452Q》L0748L35x5.545x(267+143)327+9664今32x25586-45x81^273,68^46+632604x24－758604x24－7580L425<0L38t0,01528子0.75x0.25(2448+864)今23727+9660^30x2558-45x80子25368今46+632644x14－858408x59478x39278x39478x1910.8/15+7/3-8/5408－12x2446+28)x6042x50-1715今10.8/15+7/3-8/5408－12x2446+28)x6042x50-1715今53