1. 直接写出得数。
3.5 + 4.2 = 6 - 0.5 = 2.7 - 0.4 =
0.8 + 0.7 = 4.5 - 3 = 7.8 - 1.81 =
5.1×2 = 7.2×0.2 = 3.86×10 =
3.9×0.01 = 9.73÷10 = 98.4÷100 =
1.2 + 0.3 = 5.4 - 2.3 = 0.65 + 0.35 =
6.85 + 1.05 = 4.89 - 2.7 = 10 - 9.9 =
4.2 - 4 = 5.1 - 2.1 = 4.3 + 2.7 =

3.5 + 4.2 = 7.7
6 - 0.5 = 5.5
2.7 - 0.4 = 2.3
0.8 + 0.7 = 1.5
4.5 - 3 = 1.5
7.8 - 1.81 = 5.99
5.1×2 = 10.2
7.2×0.2 = 1.44
3.86×10 = 38.6
3.9×0.01 = 0.039
9.73÷10 = 0.973
98.4÷100 = 0.984
1.2 + 0.3 = 1.5
5.4 - 2.3 = 3.1
0.65 + 0.35 = 1
6.85 + 1.05 = 7.9
4.89 - 2.7 = 2.19
10 - 9.9 = 0.1
4.2 - 4 = 0.2
5.1 - 2.1 = 3
4.3 + 2.7 = 7

2. 计算下列各题，能简算的要简算。
25 - 10.83 + 6.5 30.7 - (7.24 + 5.87) 25.19 - (15.25 + 5.19)
4.9 - 3.9×1.02 4.4×2.5 99×0.4 + 0.4

25 - 10.83 + 6.5
=14.17 + 6.5
=20.67
30.7 - (7.24 + 5.87)
=30.7 - 13.11
=17.59
25.19 - (15.25 + 5.19)
=25.19 - 5.19 - 15.25
=20 - 15.25
=4.75
4.9 - 3.9×1.02
=4.9 - (3.9×1 + 3.9×0.02)
=4.9 - (3.9 + 0.078)
=4.9 - 3.978
=0.922
4.4×2.5
=(4 + 0.4)×2.5
=4×2.5 + 0.4×2.5
=10 + 1
=11
99×0.4 + 0.4
=(99 + 1)×0.4
=100×0.4
=40

3. 不改变数的大小，把下面的数改写成三位小数。
0.07 = 7.31 = 2 = 8.75 =
1.03 = 10.02 = 1.1 = 41.06 =

0.07 = 0.070
7.31 = 7.310
2 = 2.000
8.75 = 8.750
1.03 = 1.030
10.02 = 10.020
1.1 = 1.100
41.06 = 41.060