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

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

$8.8×1.2$ $\boldsymbol{＞}$ $8.8$
$0.25×4$ $\boldsymbol{＜}$ $2.5×0.5$
$0.83×0.1$ $\boldsymbol{＜}$ $0.83$

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？

60×0.4=24（分）
260×24=6240（个）
60×1.5=90（分）
260×90=23400（个）
答：0.4时能打6240个字，1.5时能打23400个字。