ABCD is a parallelogram in which ∠DAO=40∘,∠BAO=35∘ and ∠COD=65∘ . Find ∠ODC.
∠AOB=∠COD=65∘ [Vertically Opposite Angles] In ΔAOB,∠OAB+∠AOB+∠ABO=180∘ ⇒35∘+65∘+∠OBA=180∘ ⇒∠OBA=80∘ ∠ODC=∠OBA=80∘ [Alternate interior angles as DC ∥ AB.]