1. 直接写出得数。
0.4×0.5=
0.9×0.9=
1.8×0.1=
1.2×0.07×10=
3×0.9=
4×0.6=
0.7×0.8=
0.6×80×0.3=
2.1×0.4=
2.2×0.04=
0.6×0.02=
5.1×0.2×0.1=
3.1×0.02=
1.5×0.9=
0.32×0.5=
7.5×100×0.01=
0.32×0.3=
2.4×0.5=
0.19×0.4=
0.125×8×0.2=
4×0.05=
0.8×0.21=
1.05×0.2=
0.7×0.8×0.3=
0.6×1.3=
1.6×0.02=
5×2.8=
0.4×0.02×1.3=
4.8×0.2=
0.52×0.4=
7.2×0.3=
0.5×0.3×0.8=

1. 0.2
0.81
0.18
0.84
2.7
2.4
0.56
14.4
0.84
0.088
0.012
0.102
0.062
1.35
0.16
7.5
0.096
1.2
0.076
0.2
0.2
0.168
0.21
0.168
0.78
0.032
14
0.0104
0.96
0.208
2.16
0.12

2. 用竖式计算。
5.8×1.9=
2.4×7.8=
1.5×0.36=
4.08×1.2=
6.62×5.5=
90.2×6.7=

2. 11.02 18.72 0.54
4.896 36.41 604.34
竖式略

（1）若 $ a = 0.\underbrace{00···0}_{100个0}5, b = 0.\underbrace{00···0}_{100个0}3, 则 a × b = (\quad) $。
（2）若 $ a = 0.\underbrace{00···0}_{2025个0}8, b = 0.\underbrace{00···0}_{2024个0}25, 则 a × b = (\quad) $。

(1) $0.\underbrace{00···0}_{200个0}15$
(2) $0.\underbrace{00···0}_{4049个0}2$