1.口算。
0.3×17=
7.5×0.8=
3×1.2=
5.7×4=
0.38×0.2=
6.5×6=
4×0.12=
3.2×3=

0.3×17=5.1
7.5×0.8=6
3×1.2=3.6
5.7×4=22.8
0.38×0.2=0.076
6.5×6=39
4×0.12=0.48
3.2×3=9.6

2.竖式计算。(带*的结果保留两位小数)
13.6×24
31.5×2.2
0. 35×2.06
4.8×6.55
7.8×1.25
0. 85×1.12

13.6×24=326.4
```
13.6
× 24
--------
544
272
--------
326.4
```
31.5×2.2=69.3
```
31.5
× 2.2
--------
630
630
--------
69.30
```
*0.35×2.06≈0.72
```
2.06
× 0.35
--------
1030
618
--------
0.7210
```
4.8×6.55=31.44
```
6.55
× 4.8
--------
5240
2620
--------
31.440
```
7.8×1.25=9.75
```
1.25
× 7.8
--------
1000
875
--------
9.750
```
*0.85×1.12≈0.95
```
1.12
× 0.85
--------
560
896
--------
0.9520
```

3.不计算，直接在○里填“＞”“＜”或“=”。
8.8×1.2 ○8.8
0.25×4 ○2.5×0.5
0.83×0.1 ○0.83

8.8×1.2 ＞ 8.8
0.25×4 ＜ 2.5×0.5
0.83×0.1 ＜ 0.83

4.怎样简便怎样算。
0.25×1.7×4×0.3
1.25×0.25×0.4×0.8

0.25×1.7×4×0.3
=(0.25×4)×(1.7×0.3)
=1×0.51
=0.51
1.25×0.25×0.4×0.8
=(1.25×0.8)×(0.25×0.4)
=1×0.1
=0.1

5.王明每分能打260个字，0.4时能打多少个字？1.5时呢？

0.4时 = 24分
260×24 = 6240（个）
1.5时 = 90分
260×90 = 23400（个）
答：0.4时能打6240个字，1.5时能打23400个字。