1. 直接写出得数。
$0.3×0.23=$ $1.03×0.6=$ $0.25×4=$
$0.8×50=$ $0.22×5=$ $0.16×200=$
$80.08×1000=$ $1.5×80=$ $0.75×0.2=$
$0.5×4.8=$ $10.5×8=$ $5.05×0.8=$
$20×0.51=$ $0.021×9=$ $45×0.2=$
$5.5×0.2=$ $0.05×800=$ $3.05×0.2=$

$0.3×0.23=0.069$
$1.03×0.6=0.618$
$0.25×4=1$
$0.8×50=40$
$0.22×5=1.1$
$0.16×200=32$
$80.08×1000=80080$
$1.5×80=120$
$0.75×0.2=0.15$
$0.5×4.8=2.4$
$10.5×8=84$
$5.05×0.8=4.04$
$20×0.51=10.2$
$0.021×9=0.189$
$45×0.2=9$
$5.5×0.2=1.1$
$0.05×800=40$
$3.05×0.2=0.61$

2. 列竖式计算，带★的要验算。
$2.17×0.37=$ $500×4.34=$ ★$0.55×0.68=$
$2.25×1.5=$ $1.08×2.5=$ $2.48×1.46=$

$2.17×0.37=0.8029$
$\begin{array}{r}2.17\\×0.37\\\hline1519\\651\\\hline0.8029\end{array}$
$500×4.34=2170$
$\begin{array}{r}4.34\\×\ \ 500\\\hline2170.00\end{array}$
★$0.55×0.68=0.374$
$\begin{array}{r}0.55\\×0.68\\\hline440\\330\\\hline0.3740\end{array}$
验算：
$\begin{array}{r}0.68\\×0.55\\\hline340\\340\\\hline0.3740\end{array}$
$2.25×1.5=3.375$
$\begin{array}{r}2.25\\×\ 1.5\\\hline1125\\225\\\hline3.375\end{array}$
$1.08×2.5=2.7$
$\begin{array}{r}1.08\\×\ 2.5\\\hline540\\216\\\hline2.700\end{array}$
$2.48×1.46=3.6208$
$\begin{array}{r}2.48\\×1.46\\\hline1488\\992\\248\\\hline3.6208\end{array}$

3. 计算下列各题，能简算的要简算。
$1.25×0.9×0.8$ $4.89×99+4.89$ $9.6×10.1$
$5.35-1.25-0.75$ $3.36+4.8+2.64+3.2$ $2.5×3.2×12.5$

1.25×0.9×0.8
=1.25×0.8×0.9
=1×0.9
=0.9
4.89×99+4.89
=4.89×(99+1)
=4.89×100
=489
9.6×10.1
=9.6×(10+0.1)
=9.6×10+9.6×0.1
=96+0.96
=96.96
5.35-1.25-0.75
=5.35-(1.25+0.75)
=5.35-2
=3.35
3.36+4.8+2.64+3.2
=(3.36+2.64)+(4.8+3.2)
=6+8
=14
2.5×3.2×12.5
=2.5×(0.4×8)×12.5
=(2.5×0.4)×(8×12.5)
=1×100
=100