20. Calculate: $1101_{(2)} \times 101_{(2)}=$ $\qquad$ (2).
Analysis: Binary: carry 1 when full 2. Multiplication follows the rules of decimal multiplication.
$$
\begin{array}{r}
1101 \\
\times \quad 101 \\
\hline 1101 \\
1101 \\
\hline 1000001 \\
(1101)_{2} \times(101)_{2}=(1000001)_{2}
\end{array}
$$