一、口算。
$4÷0.25 = $ $3.2×0.5 = $ $6.72 - (0.38 + 1.72) = $
$1.9 + 4.01 = $ $8.8÷0.11 = $ $4×1.2×0.25 = $
$0.125×8 = $ $1.8×40 = $ $2.5 - 3.6÷1.8 = $
$3.2÷0.04 = $ $4.08 + 5.2 = $ $16 - 4.5 - 5.5 = $
$4.2×3 = $ $70÷3.5 = $ $1.9 + 5.1÷51 = $
$1.2×0.8 = $ $3.6 - 0.36 = $ $0.8 - 0.8÷2 = $
$\frac{4}{5} - \frac{1}{2} = $ $\frac{9}{20} + \frac{2}{5} = $ $\frac{7}{5} - \frac{2}{3} - \frac{1}{3} = $
$\frac{1}{2} + \frac{4}{11} = $ $\frac{9}{10} - \frac{3}{8} = $ $\frac{7}{11} - \frac{1}{5} + \frac{4}{11} = $

16 1.6 4.62 5.91 80 1.2 1 72 0.5 80 9.28 6 12.6 20 2 0.96 3.24 0.4 $\frac{3}{10}$ $\frac{17}{20}$ $\frac{2}{5}$ $\frac{19}{22}$ $\frac{21}{40}$ $\frac{4}{5}$

$4÷0.25 = 16$
$3.2×0.5 = 1.6$
$6.72 - (0.38 + 1.72) = 4.62$
$1.9 + 4.01 = 5.91$
$8.8÷0.11 = 80$
$4×1.2×0.25 = 1.2$
$0.125×8 = 1$
$1.8×40 = 72$
$2.5 - 3.6÷1.8 = 0.5$
$3.2÷0.04 = 80$
$4.08 + 5.2 = 9.28$
$16 - 4.5 - 5.5 = 6$
$4.2×3 = 12.6$
$70÷3.5 = 20$
$1.9 + 5.1÷51 = 2$
$1.2×0.8 = 0.96$
$3.6 - 0.36 = 3.24$
$0.8 - 0.8÷2 = 0.4$
$\frac{4}{5} - \frac{1}{2} = \frac{3}{10}$
$\frac{9}{20} + \frac{2}{5} = \frac{17}{20}$
$\frac{7}{5} - \frac{2}{3} - \frac{1}{3} = \frac{2}{5}$
$\frac{1}{2} + \frac{4}{11} = \frac{19}{22}$
$\frac{9}{10} - \frac{3}{8} = \frac{21}{40}$
$\frac{7}{11} - \frac{1}{5} + \frac{4}{11} = \frac{4}{5}$

二、计算下面各题,怎样简便就怎样计算。
$7.25×0.4 + 12.75×0.4$ $9.2×3.6÷15$ $(39 - 11.4)÷(13.8÷0.6)$
$306÷0.4÷25$ $0.9 + 9.9 + 99.9$ $9.85 - (4×1.15 + 1.85)$

8 2.208 1.2 30.6 110.7 3.4

1. $7.25×0.4 + 12.75×0.4$
$=(7.25 + 12.75)×0.4$
$=20×0.4$
$=8$
2. $9.2×3.6÷15$
$=33.12÷15$
$=2.208$
3. $(39 - 11.4)÷(13.8÷0.6)$
$=27.6÷23$
$=1.2$
4. $306÷0.4÷25$
$=306÷(0.4×25)$
$=306÷10$
$=30.6$
5. $0.9 + 9.9 + 99.9$
$=(1 - 0.1) + (10 - 0.1) + (100 - 0.1)$
$=1 + 10 + 100 - 0.1×3$
$=111 - 0.3$
$=110.7$
6. $9.85 - (4×1.15 + 1.85)$
$=9.85 - (4.6 + 1.85)$
$=9.85 - 6.45$
$=3.4$