7種常考題型一、乘法分配律(1.25-0.125)×8

(125+2.5)×0.8

3.72×3.5+6.28×3.5=1.25×8-0.125×8

=125×0.8+2.5×0.8

=3.5×(3.5+6.28)=10-1

=1+1

=3.5×10=9

(正用)

=2

(正用)

=35

(逆用)二、乘法交換律0.25×8.5×4

12.5×0.96×0.8

0.5×0.34×0.6=0.25×4×8.5

=12.5×0.8×0.96

=0.5×0.6×0.34=1×8.5

=10×0.96

=0.3×0.34=8.5

=9.6

=0.102三、乘法結(jié)合律4.36×12.5×8

0.95×0.25×4

0.75×50×0.4=4.36×(12.5×8)

=0.95×(0.25×4)

=0.75×(50×0.4)=4.36×100

=0.95×1

=0.75×20=436

=0.95

=15四、拆數(shù)+乘法結(jié)合律0.125×8.8

0.25×0.28

0.125×3.2×2.5=0.125×8×1.1

=0.25×4×0.07

=(0.125×8)×(0.4×2.5)=1×1.1

=1×0.07

=1×1=1.1

=0.07

=17種?？碱}型五、把其中一個(gè)因數(shù)分成兩個(gè)數(shù)的和或差，再按乘法分配律0.8×100.1

3.65×10.1

0.32×403=0.8×(100+0.1)

=3.65×(10+0.1)

=0.32×(400+3)=0.8×100+0.8×0.1

=3.65×10+3.65×0.1

=0.32×400+0.32×3=80+0.08

=36.5+0.365

=128+0.96=80.08

=36.865

=128.96六、更改因數(shù)的小數(shù)點(diǎn)位置6.66×3.3+0.666×67

46×57+23×86

4.8×7.8+78×0.52=6.66×3.3+6.66×6.7

=46×57+46×43

=4.8×7.8+7.8×5.2=6.66×(3.3+6.1)

=46×(57+43)

=7.8×(4.8+5.2)=6.66×10

=46×100

=7.8×10=66.6

=4600

=78七、添加因數(shù)“1”56.5×99+56.5

9.7×99+9.7

4.2×99+4.2=56.5×99+56.5×1

=9.7×99+9.7×1

=4.2×99+4.2×1=56.5×(99+1)

=9.7×(99+1)

=4.2×(99+1)=56.5×100

=9.7×100

=4.2×100=5650

=970

=420常考專項(xiàng)練習(xí)題1.直接寫出得數(shù)。0.6×0.8=0.483×0.9=2.7

2.5×0.4=1

3.6×0.4=1.4412.5×8=100

50×0.04=2

80×0.3=24

1.1×9=9.92.列豎式計(jì)算。3.6×9.7=34.924.26×0.3=1.2780.35×2.03≈0.71（保留兩位小數(shù)）3.用簡(jiǎn)便方法計(jì)算下面各題。1.25×3.4×8

2.56×2.4+7.44×2.4

=1.25×8×3.4

=（2.56+7.44）×2.4=10×3.4

=10×2.4=34

=243.58×1014.5×6.3+0.55×63=3.58×（100+1）

=4.5×6.3+5.5×6.3=3.58×100+3.58×1=（4.5+5.5）×6.3=358+3.58

=10×6.3

=361.58=63?？紝ｍ?xiàng)應(yīng)用題1.隨著改革開放的發(fā)展,我國(guó)出國(guó)留學(xué)的人數(shù)不斷增加。2008年出國(guó)留學(xué)的人數(shù)為17.98萬人,2013年約是2008年的2.3倍,2013年出國(guó)留學(xué)人數(shù)大約是多少萬人?(得數(shù)保留兩位小數(shù))17.98×2.3≈41.35(萬人)2.商店運(yùn)進(jìn)14筐蘋果,每筐35.8kg,賣掉了400kg,還剩下多少千克?35.8×14-400=101.2(kg)3.某藥廠生產(chǎn)的感冒靈顆粒,一盒內(nèi)裝10袋,每袋含“對(duì)乙酰氨基酚”0.2g。兩盒感冒靈顆粒含“對(duì)乙酰氨基酚”多少克?

10×2×0.2=4(g)4.蜜蜂的飛行速度可達(dá)每分鐘0.7千米，鷹的速度大約是蜜蜂速度的3.8倍。鷹的速度每分鐘是多少千米?0.7×3.8=2.66（千米）答：鷹的速度每分鐘是2.66千米。?？紝ｍ?xiàng)應(yīng)用題(1)小麗買8個(gè)包子和2個(gè)煎雞蛋,需要多少錢?0.8×8+2.5×2=11.4(元)(2)請(qǐng)你為自己選一份健康、科學(xué)的早餐,并計(jì)算一共需要多少元。答案不唯一,如:買一碗粥、5個(gè)包子和一個(gè)煎雞蛋。5.8+(5×0.8)+2.5=12.3(元)6.一長(zhǎng)方形草壇的長(zhǎng)是16米，寬是長(zhǎng)的0.8倍。長(zhǎng)方形草壇的周長(zhǎng)是多少米？面積是多少平方米？16×0.8=12.8（米）長(zhǎng)方形的周長(zhǎng)=（16+12.8）×2=57.6（米）長(zhǎng)方形的面積=16×12.8