Question

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Answer 1

Step-by-step explanation:

Angle formed at the circumference of the circle is half of the angle formed at the center of the same circle.

Hence,

$m\angle ADC = \frac{1}{2} \times m\angle ABC \\ \\ \therefore \: m\angle ADC = \frac{1}{2} \times 40 \degree \\ \\ \therefore \:m\angle ADC = 20 \degree$