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# 五年级第二单元 2

1、用简便方法计算下面各题

0.98×101 12.5 ×(8-0.8) 2.7×4.3+5.7×2.7 = 0.98×（100+1） ×100+0.98×1 = 0.98

= 98+0.98 = 98.98

= 0.77×（100--1） = 12.5×8-12.5×0.8 = 100+10 = 90 = 2.7×(4.3+5.7) = 12.5×8-12.5×0.8= 2.7×10 = 27 0.77×99 6.18×9.9+0.618 0.25×1.25×0.8×40 ×100--0.77×1 = 0.77

= 77--0.77

= 76.23 = 0.618×9.9×10+0.68×1 = 0.618×(9.9×10+1) = 0.618×(99+1) = 0.618×100 = 61.8

= 12.5×0.8×4.9

= 10×4.9

= 49 = (0.25×40)×(1.25×0.8) = 10×1 = 10 38×10.1 12.5×4.9×0.8 3.08×41-3.08 = 38×(10+0.1) × 10+38×0.1 = 38= 380+3.8 3.8 = 38= 3.08×41--3.08×1 = 3.08×(41--1) = 3.08×40 = 123.2

5.4×2.08+56×0.208-2.08

= 5.4×0.208×10+56×0.208-0.208×10

= 0.208×(5.4×10+56-10)

= 0.208×(54+56-10)

= 0.208×100

= 20.8

2、列竖式计算

9.42×7.61= 8.3×0.53= 4.18×55.5= 验算：

2.85×2.27≈ 0.037×730≈ 4026×0.79≈ （保留一位小数） （保留两位小数） （保留两位小数）

3、求下列各题的商的近似值。（列竖式）

（1）保留两位小数

6．33÷32.2≈ 1.2÷0.62≈ 7.8 ÷ 3.62≈ 5.36 ÷ 10.3≈

（2）保留一位小数

83.68 ÷ 0.84 ≈ 5.32 ÷ 0.5 ≈ 3.92 ÷ 4.5≈ 10.8 ÷ 7.02≈

(2) 求下列各题的商的近似值,是循环小数的用循环小数表示。（列竖式）

5.5 ÷0.3= 78.6 ÷ 11 = 4.1 ÷ 0.12 = 400 ÷ 75=

13.5 ÷ 11= 7.6 ÷ 4.5 = 19.4 ÷ 2.4 = 6.8 ÷ 11=