Let us consider the following equations:
$x_1+x_2+\dots+x_n=1$ where $x_i\in \{0,1\}$ How can I determine all the solutions? I can solve easily the equation of two varieties like this:
$x_1+x_2=1$. Here the the number of solutions is $2$ and the solutions are $ (0,1), (1,0)$.
If at least two elements is greater than $0$ then the sum cannot be $1$, hence exactly one element is $1$, hence there are n solutions, depending on which of the number is $1$.