一、口算。
80 - 20 =
7 × 9 =
10 - 2 × 3 =
69 + 12 =
880 + 12 =
6 × 6 + 9 =
5 × 5 =
360 + 40 =
8 + 4 × 3 =
77 - 8 =
11 × 9 =
4 × 5 - 1 =
62 - 35 =
45 + 9 =
3 + 7 × 7 =
8 × 4 =
64 - 30 =
2 × 9 - 5 =
43 + 57 =
642 - 301 =
8 × 6 + 2 =
32 × 2 =
1200 - 500 =
27 - 9 × 3 =

1. 80 - 20 = 60
2. 7 × 9 = 63
3. 10 - 2 × 3 = 4
4. 69 + 12 = 81
5. 880 + 12 = 892
6. 6 × 6 + 9 = 45
7. 5 × 5 = 25
8. 360 + 40 = 400
9. 8 + 4 × 3 = 20
10. 77 - 8 = 69
11. 11 × 9 = 99
12. 4 × 5 - 1 = 19
13. 62 - 35 = 27
14. 45 + 9 = 54
15. 3 + 7 × 7 = 52
16. 8 × 4 = 32
17. 64 - 30 = 34
18. 2 × 9 - 5 = 13
19. 43 + 57 = 100
20. 642 - 301 = 341
21. 8 × 6 + 2 = 50
22. 32 × 2 = 64
23. 1200 - 500 = 700
24. 27 - 9 × 3 = 0

二、计算下面各题。
$4×9+21$
$21×4+12$
$34+7×8$
$3×8-19$
$79-6×10$
$22×4-63$

1. $4×9+21=57$
2. $21×4+12=96$
3. $34+7×8=90$
4. $3×8-19=5$
5. $79-6×10=19$
6. $22×4-63=25$