binary to decimal tip

how to convert binary to decimal in your mind very easily

You only need to remember 2 things:

(1) the first 8 numbers:
000 0
001 1
010 2
011 3
100 4
101 5
110 6
111 7

(2) shifting to left by one digit multiplies the number by 2 (10b):
1010 = 101 x 10 = 5 x 2 = 10
10100 = 101 x 100 = 5 x 4 = 20
101000 = 101 x 1000 = 5 x 8 = 40

When you see something like 101011, you can process it this way:
101011 = 101000 + 11 = 5 * 8 + 3 = 43

1110101 = 7 * 16 + 5 = 117
and so on.

It is easier than it looks at first glance :)

source: vik korneev at http://catonmat.net/blog/low-level-bit-hacks-you-absolutely-must-know/