Evaluate (3+-1)/2

Replace all occurrences of ${\displaystyle +}$${\displaystyle -}$ with a single ${\displaystyle -}$. A plus sign followed by a minus sign has the same mathematical meaning as a single minus sign because ${\displaystyle 1\cdot -1=-1}$

Subtract ${\displaystyle 1}$ from ${\displaystyle 3}$.