算一算。
$\begin{array}{r} 131\\ ×\ $$1\\ \hline \end{array}$
$\begin{array}{r} 142\\ ×\ $$5\\ \hline \end{array}$
$\begin{array}{r} 233\\ ×\ $$5\\ \hline \end{array}$
$\begin{array}{r} 158\\ ×\ $$1\\ \hline \end{array}$
$\begin{array}{r} 531\\ ×\ $$2\\ \hline \end{array}$
$\begin{array}{r} 420\\ ×\ $$5\\ \hline \end{array}$

1. 2751
2. 2130
3. 10485
4. 9638
5. 22302
6. 10500

用竖式计算。
$243×21=$
$107×14=$
$340×52=$
$228×75=$
$309×72=$
$480×25=$

1. $243×21=5103$
2. $107×14=1498$
3. $340×52=17680$
4. $228×75=17100$
5. $309×72=22248$
6. $480×25=12000$