Borrowing from this question. How many ways are there to represent a 3 binary digit number that starts with 1 XOR ends with 0? I calculated the following:
- number of ways to start with 1xx :$2^2$
- number of ways to end with xx0: $2^2$
- number of ways for both 1x0 : $2^1$
Mathematically I got the answer as $2^2 +2^2-2^1 = 6$ but using a tree diagram I found only 4 possible combinations: that is 101 111 000 010
I would like some help to pinpoint where I went wrong.