12. In daily life, we often use the decimal system to represent numbers, which uses 10 digits: $0,1,2,3,4,5,6,7,8,9$. In electronic computers, the binary system is used, which only requires two digits: 0 and 1.
Just as in the decimal system, addition involves "carrying over when reaching ten," in the binary system, "carrying over when reaching 2" is necessary. Thus, we can obtain the following table comparing the decimal and binary representations of natural numbers:
\begin{tabular}{|l|l|l|l|l|l|l|l|l|l|l|}
\hline Decimal & 0 & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & $\cdots$ \\
\hline Binary & 0 & 1 & 10 & 11 & 100 & 101 & 110 & 111 & 1000 & $\cdots$ \\
\hline
\end{tabular}

The decimal 0 is still 0 in binary, the decimal 1 is still 1 in binary, the decimal 2 becomes $1+1=10$ in binary, the decimal 3 becomes $10+1=11$ in binary, and so on.
So, the binary number “11110” in decimal is
【考点】Base Conversion
【难度】 $\sqrt{n}$

【答案】 30
【解答】Binary to Decimal.