1. 直接写出得数。
$3.14×3=$
$3.14×5=$
$31.4÷3.14=$
$3.14×0.2=$
$3.14×0.6=$
$10×\dfrac{7}{15}=$
$7.8÷3=$
$25.12÷8=$
$0÷3.14=$

$3.14×3=9.42$
$3.14×5=15.7$
$31.4÷3.14=10$
$3.14×0.2=0.628$
$3.14×0.6=1.884$
$10×\dfrac{7}{15}=\dfrac{14}{3}$（或$4\dfrac{2}{3}$）
$7.8÷3=2.6$
$25.12÷8=3.14$
$0÷3.14=0$

2. 脱式计算。（能简算的要简算）
$24×\dfrac{2}{5}×\dfrac{5}{8}$
$\dfrac{2}{9}÷\dfrac{2}{3}÷\dfrac{3}{5}$
$\dfrac{3}{8}÷(1÷\dfrac{2}{3})$
$27×(1+\dfrac{2}{3})$
$3÷(\dfrac{1}{4}×\dfrac{3}{5})$
$\dfrac{2}{7}×(\dfrac{1}{5}÷\dfrac{1}{3})$

$24×\dfrac{2}{5}×\dfrac{5}{8}$
$=24×(\dfrac{2}{5}×\dfrac{5}{8})$
$=24×\dfrac{1}{4}$
$=6$
$\dfrac{2}{9}÷\dfrac{2}{3}÷\dfrac{3}{5}$
$=\dfrac{2}{9}×\dfrac{3}{2}×\dfrac{5}{3}$
$=\dfrac{1}{3}×\dfrac{5}{3}$
$=\dfrac{5}{3}$
$\dfrac{3}{8}÷(1÷\dfrac{2}{3})$
$=\dfrac{3}{8}÷\dfrac{3}{2}$
$=\dfrac{3}{8}×\dfrac{2}{3}$
$=\dfrac{1}{4}$
$27×(1+\dfrac{2}{3})$
$=27×1+27×\dfrac{2}{3}$
$=27+18$
$=45$
$3÷(\dfrac{1}{4}×\dfrac{3}{5})$
$=3÷\dfrac{3}{20}$
$=3×\dfrac{20}{3}$
$=20$
$\dfrac{2}{7}×(\dfrac{1}{5}÷\dfrac{1}{3})$
$=\dfrac{2}{7}×(\dfrac{1}{5}×3)$
$=\dfrac{2}{7}×\dfrac{3}{5}$
$=\dfrac{6}{35}$

3. 解方程。
$x÷0.3=1.2$
$4.5-x=2.5$
$0.25x=25$

解：$x÷0.3=1.2$
$x=1.2×0.3$
$x=0.36$
解：$4.5-x=2.5$
$x=4.5-2.5$
$x=2$
解：$0.25x=25$
$x=25÷0.25$
$x=100$

4. 解比例。
$x:5=\dfrac{1}{5}:\dfrac{1}{9}$
$\dfrac{15}{2}=\dfrac{7}{x}$
$30:0.1=x:20$

解：$\dfrac{1}{9}x = 5×\dfrac{1}{5}$
$\dfrac{1}{9}x = 1$
$x = 1÷\dfrac{1}{9}$
$x = 9$
解：$15x = 2×7$
$15x = 14$
$x = \dfrac{14}{15}$
解：$0.1x = 30×20$
$0.1x = 600$
$x = 600÷0.1$
$x = 6000$