302 in decimal = 3x100 + 0x10 + 2x1
11001 in binary = 1x16 + 1x8 + 0x4 + 0x2 + 1x1 = 25.
You could think of it like this.
3x10^2 + 0x10^1 + 2x10^0
1x2^4 + 1x2^3 + 0x2^2 + 1x2^1 + 1x2^0
(^ mean to the power of what ever base you want. Binary is base 2, so you ^ every from that base)