# In the given figure, AB || CD. If ∠AOC = 30° and ∠OAB = 100°, then ∠OCD = ?A. 130°B. 150°C. 80°D. 100°

From O, draw E such that OE || CD || AB.

OE || CD and OC is traversal.

So,

DCO + COE = 180 (co –interior angles)

x + COE = 180

COE = (180 – x)

Now, OE || AB and AO is the traversal.

BAO + AOE = 180 (co –interior angles)

BAO + AOC + COE = 180

100 + 30 + (180 – x) = 180

180 – x = 50

X = 180 – 50 = 130O

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