算一算
$16 × \dfrac{5}{8} =$
$18 × \dfrac{5}{9} =$
$20 × \dfrac{9}{10} =$
$22 × \dfrac{9}{11} =$
$8 × \dfrac{11}{12} =$
$25 × \dfrac{8}{15} =$
$35 × \dfrac{13}{15} =$
$12 × \dfrac{15}{16} =$
$12 × \dfrac{19}{20} =$
$14 × \dfrac{2}{21} =$

16×$\dfrac{5}{8}$ = (16÷8)×5 = 2×5 = 10
18×$\dfrac{5}{9}$ = (18÷9)×5 = 2×5 = 10
20×$\dfrac{9}{10}$ = (20÷10)×9 = 2×9 = 18
22×$\dfrac{9}{11}$ = (22÷11)×9 = 2×9 = 18
8×$\dfrac{11}{12}$ = (8÷4)×$\dfrac{11}{3}$ = 2×$\dfrac{11}{3}$ = $\dfrac{22}{3}$
25×$\dfrac{8}{15}$ = (25÷5)×$\dfrac{8}{3}$ = 5×$\dfrac{8}{3}$ = $\dfrac{40}{3}$
35×$\dfrac{13}{15}$ = (35÷5)×$\dfrac{13}{3}$ = 7×$\dfrac{13}{3}$ = $\dfrac{91}{3}$
12×$\dfrac{15}{16}$ = (12÷4)×$\dfrac{15}{4}$ = 3×$\dfrac{15}{4}$ = $\dfrac{45}{4}$
12×$\dfrac{19}{20}$ = (12÷4)×$\dfrac{19}{5}$ = 3×$\dfrac{19}{5}$ = $\dfrac{57}{5}$
14×$\dfrac{2}{21}$ = (14÷7)×$\dfrac{2}{3}$ = 2×$\dfrac{2}{3}$ = $\dfrac{4}{3}$

1. 把5 g盐溶入10 g水中,盐占盐水的()。

A.$\frac{1}{10}$
B.$\frac{1}{15}$
C.$\frac{1}{3}$

1. C

2. 一筐橘子售出$\frac{7}{9}$后,还剩10 kg。这筐橘子重多少千克?正确的列式是()。

A.$10×(1-\frac{7}{9})$
B.$10÷\frac{7}{9}$
C.$10÷(1-\frac{7}{9})$

2. C

3. 一段2 m长的绳子,第一次用去全长的$\frac{1}{5}$,第二次用去$\frac{2}{5}$ m,两次用的绳子长度相比,()。

A.第二次用得多
B.两次用的一样多
C.无法确定

3. B

二、解方程。
$\frac{3}{8}x = \frac{2}{15} + \frac{3}{5}$
$\frac{5}{9}x - \frac{1}{4} = \frac{3}{4}$

1.$x = \frac{88}{45}$
2.$x = \frac{9}{5}$

三、看图列式计算。
1.
2.

1. $240 ÷ \frac{4}{5} =300(\mathrm{m})$
2. 小叶:$36 × \frac{5}{6} = 30(\mathrm{元})$
小慧:$30 × \frac{2}{3} = 20(\mathrm{元})$