If you have a flat symmetrical molecule such as Borane $BH_3$ then dividing $360^@$ by the number of bonds makes sense, but in the case of a three dimensional tetrahedral molecule such as Methane $CH_4$ it does not.
You could model the shape by imagining a carbon atom at $(0, 0, 0)$ and hydrogen atoms at: $(1, 1, 1)$, $(1, -1, -1)$, $(-1, 1, -1)$ and $(-1, -1, 1)$ (alternate vertices of a cube form the vertices of a tetrahedron).
Then the angle between the line joining $(0, 0, 0)$ and $(1, 1, 1)$ and the line joining $(0, 0, 0)$ and $(1, -1, -1)$ is:
$arccos((<1,1,1> . <1,-1,-1>)/(abs(<1,1,1>)*abs(<1,-1,-1>))) = arccos(-1/3) ~~ 109.5^@$
