回答如下：1. 3/5 x 20 = 12
2. 1/4 x 24 = 6
3. 5/8 x 16 = 10
4. 2/3 x 15 = 10
5. 3/4 x 12 = 9
6. 1/2 x 10 = 5
7. 5/6 x 18 = 15
8. 1/3 x 27 = 9
9. 2/5 x 25 = 10
10. 4/7 x 21 = 12
11. 3/10 x 40 = 12
12. 7/8 x 32 = 28
13. 1/6 x 36 = 6
14. 4/9 x 27 = 12
15. 2/7 x 14 = 4
16. 3/8 x 32 = 12
17. 5/9 x 45 = 25
18. 1/5 x 15 = 3
19. 4/6 x 12 = 8
20. 3/7 x 21 = 9
（4/9+8/27）×3×9
=4/9×3×9+8/27×3×9
=12+8
=20
5/6×5/9+5/6×4/9
=5/6×（5/9+4/9）
=5/6×1
=5/6
15/21×3/4+10/21×3/4-3/4
=3/4×（15/21+10/21-1）
=3/4×4/21
=1/7
36×34/35
=36×（1-1/35）
=36-36×1/35
=34 34/35
36×7/35
=（1+35）×7/35
=7/35+7
=7 7/35
3/5×（20+5/6）
=3/5×20+3/5×5/6
=12+1/2
=12.5
5/9÷5/12+4/9÷5/12
=5/9×12/5+4/9×12/5
=12/5×（5/9+4/9）
=12/5
（35+5/7）÷5
=（35+5/7）×1/5
=35×1/5+5/7×1/5
=7+1/7
=7 1/7
（5/6+3/8）÷1/48
=5/6×48+3/8×48
=40+18
=58
