What is the sum of $101_2$ and $1011_2$? Express your answer in base 2.
The rules of addition work in base 2 as well as base 10.  Carry any sum greater than 1 to the next place value: \[
\begin{array}{r@{}r@{}r@{}r@{}r}
& \text{\scriptsize{1}\hspace{0.3mm}} & \text{\scriptsize{1}\hspace{0.3mm}} & \text{\scriptsize{1}\hspace{0.3mm}} & \phantom{1} \\
& 1 & 0 & 1 & 1 \\
+ & & 1 & 0 & 1 \\ \hline
1 & 0 & 0 & 0 & 0
\end{array}
\] The sum is $\boxed{10000_2}$.