3. 用递等式计算。
$6.3÷(5.25×0.8)$ $3.8+[(4.6-0.25)÷4]$
$9.6÷0.8÷0.4$ $3.9÷(1.3×5)$ $6.8+0.75÷0.5$
$1.26÷[0.28×(2.2-0.7)]$ $44.3÷2.5-10.02$

1. 6.3÷(5.25×0.8)
=6.3÷4.2
=1.5
2. 3.8 + [(4.6 - 0.25)÷4]
=3.8 + [4.35÷4]
=3.8 + 1.0875
=4.8875
3. 9.6÷0.8÷0.4
=12÷0.4
=30
4. 3.9÷(1.3×5)
=3.9÷1.3÷5
=3÷5
=0.6
5. 6.8 + 0.75÷0.5
=6.8 + 1.5
=8.3
6. 1.26÷[0.28×(2.2 - 0.7)]
=1.26÷[0.28×1.5]
=1.26÷0.42
=3
7. 44.3÷2.5 - 10.02
=17.72 - 10.02
=7.7

4. 用简便方法计算。
$12.5×8.08$ $3.54×0.25+0.25×0.46$ $2.4÷0.5÷4$
$7.28×9.9+7.28×0.1$ $16.5×10.2-16.5×0.2$ $7.8÷5÷0.78$

1. 12.5×8.08
=12.5×(8 + 0.08)
=12.5×8 + 12.5×0.08
=100 + 1
=101
2. 3.54×0.25 + 0.25×0.46
=0.25×(3.54 + 0.46)
=0.25×4
=1
3. 2.4÷0.5÷4
=2.4÷(0.5×4)
=2.4÷2
=1.2
4. 7.28×9.9 + 7.28×0.1
=7.28×(9.9 + 0.1)
=7.28×10
=72.8
5. 16.5×10.2 - 16.5×0.2
=16.5×(10.2 - 0.2)
=16.5×10
=165
6. 7.8÷5÷0.78
=7.8÷0.78÷5
=10÷5
=2

5. 下面的计算正确吗？把错误的改正过来。
(1)$3.76×(0.25+25.8)$ (2)$12.5×8×12.5×2$
$=0.94+25.8$ $=12.5×(8+2)$
$=26.74$ $=12.5×10$
$=125$
(3)$1.56÷2.3≈0.68$ (4)$3.4÷0.05= 6.8$

【解析】：
(1)×，改正：3.76×(0.25+25.8)=3.76×26.05=97.948；
(2)×，改正：12.5×8×12.5×2=(12.5×8)×(12.5×2)=100×25=2500；
(3)×，改正：
(4)×，改正：
【答案】：
(1)×；
(2)×；
(3)√；
(4)×