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
```
计算结果0.721，保留两位小数得0.72
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
```
计算结果0.952，保留两位小数得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 ＞ 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

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