$737 ÷ 90 \approx$ $500 ÷ 60 \approx$ $399 ÷ 80 \approx$
$249 ÷ 60 \approx$ $557 ÷ 70 \approx$ $248 ÷ 30 \approx$
$123 ÷ 30 \approx$ $255 ÷ 50 \approx$ $435 ÷ 80 \approx$
$565 ÷ 80 \approx$ $186 ÷ 20 \approx$ $203 ÷ 17 \approx$

解析：本题考查除法的估算。估算时，一般要根据``四舍五入''法把数看作是整十、整百、整千······的数来进行计算。
答案：
$737 ÷ 90 \approx 720 ÷ 90 = 8$
$500 ÷ 60 \approx 540 ÷ 60 = 9$
$399 ÷ 80 \approx 400 ÷ 80 = 5$
$249 ÷ 60 \approx 240 ÷ 60 = 4$
$557 ÷ 70 \approx 560 ÷ 70 = 8$
$248 ÷ 30 \approx 240 ÷ 30 = 8$
$123 ÷ 30 \approx 120 ÷ 30 = 4$
$255 ÷ 50 \approx 250 ÷ 50 = 5$
$435 ÷ 80 \approx 400 ÷ 80 = 5$
$565 ÷ 80 \approx 560 ÷ 80 = 7$
$186 ÷ 20 \approx 180 ÷ 20 = 9$
$203 ÷ 17 \approx 204 ÷ 17 = 12$

列竖式计算。
$253 ÷ 27 = $ 9
27)253
243
---
10
253 ÷ 27 = 9……10 $459 ÷ 51 = $ 9
51)459
459
---
0
459 ÷ 51 = 9 $369 ÷ 19 = $ 19
19)369
19
---
179
171
---
8
369 ÷ 19 = 19……8
$567 ÷ 52 = $ 10
52)567
52
---
47
567 ÷ 52 = 10……47 $989 ÷ 53 = $ 18
53)989
53
---
459
424
---
35
989 ÷ 53 = 18……35 $843 ÷ 18 = $ 46
18)843
72
---
123
108
---
15
843 ÷ 18 = 46……15

```
9
27)253
243
---
10
253 ÷ 27 = 9……10
9
51)459
459
---
0
459 ÷ 51 = 9
19
19)369
19
---
179
171
---
8
369 ÷ 19 = 19……8
10
52)567
52
---
47
567 ÷ 52 = 10……47
18
53)989
53
---
459
424
---
35
989 ÷ 53 = 18……35
46
18)843
72
---
123
108
---
15
843 ÷ 18 = 46……15
```

你能用简便方法计算下面这些题吗？
$125 × 320$ $1300 ÷ 25$ $57 × 23 + 19 × 31$
$1000 - 999 + 998 - 997 + 996 - 995 + … + 4 - 3 + 2 - 1$

解析：
这些题目主要考察的是四则运算及简便运算方法，包括乘法结合律、除法的性质、乘法分配律以及数列求和等知识点。
答案:
1. $125 × 320$
$= 125 × (8 × 40)$
$= (125 × 8) × 40$
$= 1000 × 40$
$= 40000$
2. $1300 ÷ 25$
$= 1300 ÷ (5 × 5)$
$= 1300 ÷ 5 ÷ 5$
$= 260 ÷ 5$
$= 52 × 5 ÷ 5$
$= 52$
3. $57 × 23 + 19 × 31$
$= 19 × 3 × 23 + 19 × 31$
$= 19 × 69 + 19 × 31$
$= 19 × (69 + 31)$
$= 19 × 100$
$= 1900$
4. $1000 - 999 + 998 - 997 + 996 - 995 + \ldots + 4 - 3 + 2 - 1$
$= (1000 - 999) + (998 - 997) + (996 - 995) + \ldots + (4 - 3) + (2 - 1)$
$= 1 + 1 + 1 + \ldots + 1 + 1$ （共500个1）
$= 500$