一、口算。
1. $1.66 + 23.4 =$ $5.8 ÷ 0.2 =$ $30 × 90 =$
2. $45 × 0.02 =$ $0.4 + 0.29 =$ $5.08 - 2.6 =$
3. $28.8 ÷ 8 =$ $525 - 335 =$ $12.45 + 0.75 =$
4. $9.8 - 4.72 =$ $42.6 × 0.2 =$ $90 ÷ 0.06 =$
5. $0.8 + \frac{2}{7} =$ $6 ÷ \frac{9}{11} =$ $\frac{7}{12} - \frac{3}{8} =$
6. $\frac{3}{20} × \frac{8}{9} =$ $\frac{2}{3} + \frac{7}{15} =$ $\frac{8}{15} × \frac{5}{9} =$
7. $\frac{5}{6} ÷ \frac{6}{5} =$ $\frac{3}{4} × 1.6 =$ $\frac{7}{8} × \frac{4}{7} =$
8. $20 × \frac{2}{5} =$ $\frac{8}{21} × \frac{7}{16} =$ $\frac{1}{3} ÷ \frac{3}{8} =$

1. 25.06、29、2700
2. 0.049、0.69、2.48
3. 3.6、190、13.2
4. 5.08、8.52、1500
5. $\frac{38}{35}$、$\frac{22}{3}$、$\frac{5}{24}$
6. $\frac{2}{15}$、$\frac{17}{15}$、$\frac{8}{27}$
7. $\frac{25}{36}$、$\frac{6}{5}$、$\frac{1}{2}$
8. 8、$\frac{1}{6}$、$\frac{8}{9}$

二、根据比例的基本性质，在括号里填合适的数。
$(\ ):17=4:3.4$
$\frac{3}{5}:2.5=6:(\ )$
$\frac{7}{16}:(\ )=\frac{3}{8}:\frac{4}{9}$
$3:1.2=(\ ):4.8$
$\frac{3}{5}:(\ )=\frac{1}{4}:\frac{5}{6}$
$\frac{4}{9}:\frac{1}{6}=(\ ):15$
$\frac{3}{20}:0.6=6.5:(\ )$
$(\ ):\frac{4}{9}=\frac{15}{16}:\frac{1}{3}$
$0.8:(\ )=1.5:4.5$
$\frac{1}{6}:(\ )=\frac{2}{3}:\frac{4}{5}$
$16:(\ )=0.75:\frac{15}{8}$
$0.25:(\ )=1.25:40$
$\frac{2}{3}:\frac{1}{10}=\frac{5}{6}:(\ )$
$4:(\ )=\frac{8}{17}:\frac{1}{34}$
$(\ ):\frac{4}{5}=\frac{5}{12}:\frac{3}{4}$

1. 20
2. 25
3. $\frac{14}{27}$
4. 12
5. 2
6. 40
7. 26
8. $\frac{5}{4}$
9. 2.4
10. $\frac{1}{5}$
11. 40
12. 8
13. $\frac{1}{8}$
14. $\frac{1}{4}$
15. $\frac{4}{9}$