What decimal number is represented bianary number 00001001?

Well, isn't that just a happy little binary number we have here! When we look at 00001001, we can see that it represents the decimal number 9. Each place in the binary number represents a power of 2, starting from the right with 2^0, then 2^1, 2^2, and so on. So, 02^7 + 02^6 + 02^5 + 02^4 + 12^3 + 02^2 + 02^1 + 12^0 equals 9.