一、口算。
0.8 - 0.42 =
3.5 × 3 =
5 ÷ 40 =
5.6 ÷ 2 =
0.9 × 0.3 =
540 × 20 =
7.2 + 3.8 =
5.26 + 3.44 =
680 ÷ 34 =
2.4 ÷ 0.8 =
8 ÷ 0.08 =
7.2 ÷ 2.4 =
0.5 × 200 =
10 - 6.4 =
299 + 365 =
$\frac{3}{4} - \frac{1}{5} =$
$\frac{7}{8} + \frac{5}{24} =$
$\frac{22}{15} - \frac{16}{15} =$
$\frac{7}{25} + \frac{2}{5} =$
$\frac{1}{2} - \frac{1}{9} =$
$\frac{5}{6} - \frac{3}{8} =$
$\frac{1}{5} + \frac{6}{35} =$
$\frac{3}{40} + \frac{1}{8} =$
$\frac{3}{7} + \frac{1}{4} =$

1. 0.38
2. 10.5
3. 0.125
4. 2.8
5. 0.27
6. 10800
7. 11
8. 8.7
9. 20
10. 3
11. 100
12. 3
13. 100
14. 3.6
15. 664
16. $\frac{11}{20}$
17. $\frac{13}{12}$
18. $\frac{2}{5}$
19. $\frac{17}{25}$
20. $\frac{7}{18}$
21. $\frac{11}{24}$
22. $\frac{13}{35}$
23. $\frac{1}{5}$
24. $\frac{19}{28}$

二、计算下面各题，能用简便算法的就用简便算法。
$\frac{7}{8} - \frac{3}{4} + \frac{1}{6}$
$\frac{5}{12} + (\frac{8}{9} - \frac{5}{12})$
$\frac{5}{12} + \frac{11}{15} - \frac{6}{15} + \frac{7}{12}$
$\frac{5}{6} - (\frac{1}{3} + \frac{3}{10})$
$\frac{3}{10} + \frac{3}{8} - \frac{2}{5}$
$\frac{13}{9} - (\frac{5}{7} + \frac{4}{9}) - \frac{1}{7}$

1. $\frac{7}{24}$
2. $\frac{8}{9}$
3. $1\frac{1}{3}$
4. $\frac{1}{5}$
5. $\frac{11}{40}$
6. $\frac{1}{7}$