Question

S, U, N are collinear. What point is between the other two if NU = 1, SU = 2, SN = 3? NU + US = NS.

Answer 1

U is between N and S.
The order of the letters does not matter, thus:
NU = 1 and US = 2 so NS = 3.
This is only possible if NU + US = NS
Proving U is between N and S.