一、口算。
$\frac{12}{13} ÷ \frac{4}{39} =$
$\frac{3}{10} × 2.5 =$
$9 ÷ \frac{3}{5} =$
$\frac{9}{10} × \frac{4}{27} =$
$\frac{4}{5} ÷ \frac{49}{50} =$
$\frac{8}{3} × 75\% =$
$\frac{6}{7} - \frac{1}{21} =$
$54 × \frac{5}{9} =$
$\frac{4}{5} ÷ 16\% =$
$\frac{2}{5} + \frac{3}{7} =$
$\frac{3}{4} ÷ \frac{1}{4} =$
$\frac{13}{8} × \frac{2}{39} =$
$\frac{4}{7} × \frac{3}{4} =$
$\frac{5}{8} ÷ \frac{1}{12} =$
$5\% × \frac{4}{5} =$
$3.8 ÷ 19\% =$
$\frac{2}{3} - 25\% =$
$\frac{9}{11} ÷ \frac{1}{9} =$
$\frac{9}{5} ÷ \frac{5}{7} =$
$40 × 40\% =$
$\frac{5}{21} × \frac{7}{15} =$

9
0.75
15
$\frac{2}{15}$
$\frac{40}{49}$
2
$\frac{17}{21}$
30
5
$\frac{29}{35}$
3
$\frac{1}{12}$
$\frac{3}{7}$
$\frac{15}{2}$
$\frac{1}{25}$
20
$\frac{5}{12}$
$\frac{81}{11}$
$\frac{63}{25}$
16
$\frac{1}{9}$

二、计算下面各图形中涂色部分的周长和面积。
1.
16 cm
2.
2 dm

1. 周长:$3.14×16÷2+3.14×(16÷2)÷2+16÷2=45.68(\mathrm{cm})$
面积:$3.14×(16÷2)^2÷2-3.14×(16÷2÷2)^2÷2=75.36(\mathrm{cm}^2)$
2. 周长:$3.14×2÷2+2×3.14×2÷4+2=8.28(\mathrm{dm})$
面积:$3.14×2^2÷4-3.14×(2÷2)^2÷2=1.57(\mathrm{dm}^2)$