ToC | Next Labs: Cryptography. Part 1. Math Alive

## Binary Numbers

How would we count if we could only have two digits: 0 and 1? The beginning is easy. We could suggest the we would denote 0 by 0 and 1 by 1. But what should we do next?

Let's think carefully about our usual base-10 (decimal) notation.
When we write 2095, we mean 2 * 1000 + 0 * 100 + 9 * 10 + 5 * 1.
Or, if we like using exponents, 2095 = 2 * 103 + 0 * 102 + 9 * 101 + 5 * 100.
Note that each digit in the sum is a number between zero and nine; there is no need for symbols greater than 9, because ten times 10k is reckoned for by adding one to the 10k+1 place.
Binary representation works on the same principle, except that each place now represents a power of 2, i.e., 2k.
So the binary number 1101 represents 1*23+1*22+0*21+1*20=8+4+0+1=13.
Note that we only need digits 0 and 1 for binary representation (just as we only needed digits 0 to 9 in decimal representation), because two times 2k is reckoned for by adding one to the 2k+1 place.

Practice
Conversion from Binary to Decimals