1. 直接写出得数。
$13.4 - 8 =$ $23 + 4.7 =$ $10 - 2.3 =$
$5.5×0.2 =$ $0.06×0.7 =$ $1.2×5 =$
$0.05×800 =$ $0.08×25 =$ $0.6 - 0.23 =$

13.4 - 8 = 5.4
23 + 4.7 = 27.7
10 - 2.3 = 7.7
5.5×0.2 = 1.1
0.06×0.7 = 0.042
1.2×5 = 6
0.05×800 = 40
0.08×25 = 2
0.6 - 0.23 = 0.37

2. 列竖式计算，带★的要验算。
$0.28×1.5 =$ $1.44×18 =$ $100 - 33.9 =$
$3.8×2.09 =$ $4.6×500 =$ ★$0.88×0.65 =$

0.28
× 1.5
-------
140
28
-------
0.42
1.44
× 18
-------
1152
144
-------
25.92
100.0
33.9
-------
66.1
2.09
× 3.8
-------
1672
627
-------
7.942
4.6
×500
-------
2300.0
=2300
0.88
×0.65
-------
440
528
-------
0.572
验算：
0.65
×0.88
-------
520
520
-------
0.572

3. 计算下列各题，能简算的要简算。
$36 + (61.2 - 40)$ $7.5 + 2.5×1.8$
$15.61 - 2.53 - 7.47$ $2.5×3.2×12.5$

$36 + (61.2 - 40)$
$=36 + 21.2$
$=57.2$
$7.5 + 2.5×1.8$
$=7.5 + 4.5$
$=12$
$15.61 - 2.53 - 7.47$
$=15.61 - (2.53 + 7.47)$
$=15.61 - 10$
$=5.61$
$2.5×3.2×12.5$
$=2.5×(0.4×8)×12.5$
$=(2.5×0.4)×(8×12.5)$
$=1×100$
$=100$

4. 解方程。
$8x - 5x = 9$ $x - 0.6 = 3.6$ $2x + 4.2 = 8.2$
$3.8 + x = 10$ $x÷3.2 = 7$ $4x - 32 = 28$

解：8x - 5x = 9
3x = 9
x = 9÷3
x = 3
解：x - 0.6 = 3.6
x = 3.6 + 0.6
x = 4.2
解：2x + 4.2 = 8.2
2x = 8.2 - 4.2
2x = 4
x = 4÷2
x = 2
解：3.8 + x = 10
x = 10 - 3.8
x = 6.2
解：x÷3.2 = 7
x = 7×3.2
x = 22.4
解：4x - 32 = 28
4x = 28 + 32
4x = 60
x = 60÷4
x = 15