How do you convert number 3 to a binary?

Answer 1

You write the number as a sum of decreasing powers of 2. Then for each power, you write 1 if it is present in the sum and 0 if not.

So, 3 = 2 + 1 = 2^1 + 2^0

and so the binary for 3 (in decimal) is 11.

Answer 2

11, base 2