1. 直接写出得数。
$7.8×100=$ $6.9÷10=$ $2.4+5.6=$
$0.42×5=$ $3.1×6=$ $29÷100=$
$12.5×80=$ $85÷100=$ $2.03+44=$

7.8×100=780
6.9÷10=0.69
2.4+5.6=8
0.42×5=2.1
3.1×6=18.6
29÷100=0.29
12.5×80=1000
85÷100=0.85
2.03+44=46.03

2. 脱式计算。（能简算的要简算）
$17×23 - 7×23$ $2.4×(0.2 + 10)$ $72×125$
$8.6×101$ $0.75×2.3 + 0.25×2.3$

$17×23 - 7×23$
$=(17-7)×23$
$=10×23$
$=230$
$2.4×(0.2 + 10)$
$=2.4×0.2 + 2.4×10$
$=0.48 + 24$
$=24.48$
$72×125$
$=9×8×125$
$=9×(8×125)$
$=9×1000$
$=9000$
$8.6×101$
$=8.6×(100+1)$
$=8.6×100 + 8.6×1$
$=860 + 8.6$
$=868.6$
$0.75×2.3 + 0.25×2.3$
$=(0.75+0.25)×2.3$
$=1×2.3$
$=2.3$

3. 解方程。
$4.5 + 5x = 27$ $2x + 4.3×3 = 14$ $3÷4x = 2.5$

解：
5x = 27 - 4.5
5x = 22.5
x = 22.5 ÷ 5
x = 4.5
解：
2x + 12.9 = 14
2x = 14 - 12.9
2x = 1.1
x = 1.1 ÷ 2
x = 0.55
解：
4x = 3 ÷ 2.5
4x = 1.2
x = 1.2 ÷ 4
x = 0.3

4. 列竖式计算并验算。
$328÷41=$ $64.5÷75=$
$282÷32=$ $0.424÷53=$

$328÷41=8$
$\begin{array}{r}8\\41\enclose{longdiv} {328}\\\underline{328}\\0\end{array}$
验算：$8×41=328$
$64.5÷75=0.86$
$\begin{array}{r}0.86\\75\enclose{longdiv} {64.50}\\\underline{60\ 0}\\4\ 50\\\underline{4\ 50}\\0\end{array}$
验算：$0.86×75=64.5$
$282÷32=8······26$
$\begin{array}{r}8\\32\enclose{longdiv} {282}\\\underline{256}\\26\end{array}$
验算：$8×32+26=282$
$0.424÷53=0.008$
$\begin{array}{r}0.008\\53\enclose{longdiv} {0.424}\\\underline{0.424}\\0\end{array}$
验算：$0.008×53=0.424$