Answer

  1. 50°
    Solution:
    $\text{EC}\ ||\text{ AB}$ and CD is transverse to it.
    Now $\angle\text{ECD} = \angle\text{AOD} = 70^\circ$ (Corresponding angles)
    In $\angle\text{OBD}$
    $\angle\text{OBD} + \angle\text{BOD} + \angle\text{ODB} = 180^\circ$
    $\angle\text{BOD} = 180^\circ - \angle\text{AOD} = 180^\circ - 70^\circ = 110^\circ$
    $\angle\text{ODB} = 20^\circ$ (Given)
    So, $\angle\text{OBD} = 180^\circ - \angle\text{BOD} - \angle\text{ODB}$
    $= 180^\circ - 110^\circ - 20^\circ$
    $= 50^\circ$

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