A – B means A is the father of B.

A + B means A is the mother of B.

A × B means A is the sister of B.

A ÷ B means A is the daughter of B.

If M + N × O – P ÷ Q + R then how is Q related to O?

Wife

↑ or ↓ ⇒ Upward or downward line shown "generation gap" .

   =    ⇒ Double lines shown "relation b/w Husband & Wife"

   —   ⇒ single line shown "relation between them other than Husband & Wife".

Clear from M is mother of N.  O is father of P.  O and Q are couple and Q is mother of R. So, clearly Q is wife of O.