130º Solution: Construction: Through O, draw OE || AB || CD $\Rightarrow\angle\text{BAO}+\angle\text{EOA}=180^\circ$ $\Rightarrow100^\circ+\angle\text{EOA}=180^\circ$ $\Rightarrow\angle\text{EOA}=80^\circ$ So, $\angle\text{EOC}=\angle\text{EAO}-\angle\text{COA}=80^\circ-30^\circ=50^\circ$ Since CD || EO $\angle\text{OCD}+\angle\text{EOC}=1806^\circ$ $\Rightarrow\angle\text{OCD}+50^\circ=180^\circ$ $\Rightarrow\angle\text{OCD}=130^\circ$
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