This is the correct answer that I copied from the link:
3.1 Binary Fractions
As a programmer, you should be familiar with the concept of binary integers, i.e. the representation
of integer numbers as a series of bits:
12310 = 1 · 102 + 2 · 101 + 3 · 100,
4568 = 4 · 82 + 5 · 81 + 6 · 80 = 30210
10010012 = 1 · 26 + 0 · 25 + 0 · 24 + 1 · 23 + 0 · 22 + 0 · 21 + 1 · 20
= 6410 + 810 + 1 = 7310
Computers use binary because transistors only have two states. On and Off, or 1 and 0.
It's all math, and it's hard, because binary math isn't like the decimal math that we learned how to do.