五年级上册数学小数乘法和简便运算

五年级上册数学小数乘法简便计算

常见敏感算式：

125×8=100025×4=1005×2=105×4=205×6=305×8=40

数字拆分：

24=4×648=6×832=4×836=4×9

48=4×1224=20+448=40+897=100-3

98=100-299=100-1101=100+1102=100+2

一、乘法交换律

(1)2.5×9×4(2)1.5×7×6(3)0.8×1.4×12.5

=2.5×4×9=1.5×6×7=0.8×12.5×1.4

=10×9=9×7=10×1.4

=90=63=14

(4)0.5×0.34×6(5)0.25×0.46×40(6)0.8×0.46×0.5

=0.5×6×0.34=0.25×40×0.46=0.8×0.5×0.46

=3×0.34=10×0.46=0.4×0.46

=1.36=4.6=0.184

二、乘法结合律

(1)4.31×1.25×0.8(2)0.79×5×2(3)0.16×2.5×400

=4.31×1=0.79×10=0.16×1000

=4.31=7.9=160

(4)12.56×0.4×5(5)4.7×8×0.5(6)3.36×0.05×6

=12.56×2=4.7×4=3.36×0.3

=25.12=18.8=1.008

五年级上册数学小数乘法简便计算

三、乘法交换律与结合律

(1)2.5×50×0.6×0.4(2)0.8×0.04×12.5×250

=2.5×0.4×50×0.6=0.8×12.5×0.04×250

=1×30=10×10

=30=100

(3)0.6×0.125×0.8×50(4)1.5×0.4×2.5×0.2

=0.6×50×0.125×0.8=1.5×0.2×0.4×2.5

=30×0.1=0.3×1

=3=0.3

四、乘法分配律(加减法)

(1)0.64×28+72×0.64(2)3.12×0.49-0.12×0.49

=0.64×(28+72)=0.49×(3.12-0.12)

=0.64×100=0.49×3

=64=1.47

(3)6.6×5.8+3.4×5.8(4)26.45×0.4-0.4×1.45

=5.8×(6.6+3.4)=0.4×(26.45-1.45)

=5.8×10=0.4×25

=58=10

(5)1.3×2.5+0.7×2.5(6)3.62×0.08-2.37×0.08

=2.5×(1.3+0.7)=0.08×(3.62-2.37)

=2.5×2=0.08×1.25

=5=0.1

五年级上册数学小数乘法简便计算

五、乘法分配律(拆分法)

(1)0.65×101(2)5.1×99(3)0.79×102

=0.65×(100+1)=5.1×(100-1)=0.79×(100+2)

=0.65×100+0.65×1=5.1×100-5.1×1=0.79×100+0.79×2

=65+0.65=510-5.1=79+1.58

=65.65=504.9=80.58

(4)1.36×99(5)1.25×0.88(6)0.25×4.4

=1.36×(100-1)=1.25×(0.8+0.08)=0.25×(4+0.4)

=1.36×100-1.36×1=1.25×0.8+1.25×0.08=0.25×4+0.25×0.4

=136-1.36=1+0.1=1+0.1

=134.64=1.1=1.1

(7)1.25×4.8(8)2.5×36(9)0.25×2.4

=1.25×(0.8+4)=2.5×(40-4)=0.25×(2+0.4)

=1.25×0.8+1.25×4=2.5×40-2.5×4=0.25×2+0.25×0.4

=1+5=100-10=0.5+0.1

=6=90=0.6

六、混合练习

(1)0.25×6.14×0.4(2)44×0.33+56×0.33

=0.25×0.4×6.14=0.33×(44+56)

=0.1×6.14=0.33×100

=0.614=33

五年级上册数学小数乘法简便计算

(3)3.2×1.25(4)(1.25-0.5)×0.8

=0.4×8×1.25=1.25×0.8-0.5×0.8

=0.4×10=1-0.4

=4=0.6

(5)7.36×101(6)2.5×204

=7.36×(100+1)=2.5×(200+4)

=7.36×100+7.36×1=2.5×200+2.5×4

=736+7.36=500+10

=743.36=510

(7)0.32×0.125×2.5(8)3.8×0.125

=0.4×0.8×0.125×2.5=(3+0.8)×0.125

=0.4×2.5×0.8×0.125=3×0.125+0.8×0.125

=1×0.1=0.375+0.1

=0.1=0.475

五年级上册数学小数乘法简便计算

常见敏感算式：

125×8=25×4=5×2=5×4=5×6=5×8=

数字拆分：

24=48=32=36=

48=24=48=97=

98=99=101=102=

一、乘法交换律

(1)2.5×9×4(2)1.5×7×6(3)0.8×1.4×12.5

(4)0.5×0.34×6(5)0.25×0.46×40(6)0.8×0.46×0.5

二、乘法结合律

(1)4.31×1.25×0.8(2)0.79×5×2(3)0.16×2.5×400

(4)12.56×0.4×5(5)4.7×8×0.5(6)3.36×0.05×6

五年级上册数学小数乘法简便计算

三、乘法交换律与结合律

(1)2.5×50×0.6×0.4(2)0.8×0.04×12.5×250

(3)0.6×0.125×0.8×50(4)1.5×0.4×2.5×0.2

.

四、乘法分配律(加减法)

(1)0.64×28+72×0.64(2)3.12×0.49-0.12×0.49

(3)6.6×5.8+3.4×5.8(4)26.45×0.4-0.4×1.45

(5)1.3×2.5+0.7×2.5(6)3.62×0.08-2.37×0.08

五年级上册数学小数乘法简便计算

五、乘法分配律(拆分法)

(1)0.65×101(2)5.1×99(3)0.79×102

(4)1.36×99(5)1.25×0.88(6)0.25×4.4

(7)1.25×4.8(8)2.5×36