1. 填空。
(1) $\frac{1}{\_\_\_\_\_\_}×9 = 1$ $\frac{5}{6}×\_\_\_\_\_\_ = 1$
$\frac{12}{7}×\_\_\_\_\_\_ = 1$ $\frac{7}{3}×\_\_\_\_\_\_ = 1$
(2) $\frac{3}{5}$的倒数是(　　　)，$\frac{9}{8}$的倒数是(　　　)，(　　　)的倒数是15，
(　　)的倒数是$\frac{1}{12}$，$\frac{7}{8}$和(　　)互为倒数，$\frac{1}{7}$和(　　　)互为倒数。

9
5
7
3
12
7
$​\frac {5}{3}​$
$​\frac {8}{9}​$
$​\frac {1}{15}​$
12
$​\frac {8}{7}​$
7
3
4
12
5
5
25
7
5
35
9
4
36
7
3
21
8
5
40
12
7
84
5
8
40
6

2. $\frac{3}{7}×\frac{4}{5} = \frac{□×□}{□×□} = \frac{□}{□}$ $\frac{5}{9}×\frac{5}{4} = \frac{□×□}{□×□} = \frac{□}{□}$
$\frac{7}{12}×\frac{3}{7} = \frac{□×□}{□×□} = \frac{□}{□}$ $\frac{8}{5}×\frac{5}{8} = \frac{□×□}{□×□} = \frac{□}{□}$

3. 计算。
$\frac{1}{6}×\frac{2}{5}×\frac{3}{4}$ $\frac{7}{8}×\frac{3}{10}×\frac{2}{9}$ $\frac{5}{7}×56×\frac{3}{8}$
$12×\frac{5}{6}×\frac{7}{8}$ $34×\frac{5}{17}×\frac{2}{15}$ $\frac{13}{28}×\frac{7}{26}×\frac{1}{3}$

$​=\frac {1}{15}×\frac {3}{4}​$
$​=\frac {1}{20}​$
$​=\frac {21}{80}×\frac {2}{9}​$
$​=\frac {7}{120}​$
$​=40×\frac {3}{8}​$
​=15​
$​=10×\frac {7}{8}​$
$​=\frac {35}{4}​$
$​=10×\frac {2}{15}​$
$​=\frac {4}{3}​$
$​=\frac {1}{8}×\frac {1}{3}​$
$​=\frac {1}{24}​$