Solution

(a) ∠NYB = 50°, ∠YNB = 20°.

In
∆YNB,

∠NYB + ∠YNB + ∠YBN = 180o

50^o + 20^o + ∠YBN = 180^o

∠YBN + 70^o = 180^o

∠YBN = 180^o – 70^o = 110^o

But ∠MAN = ∠YBN

(Angles in the same segment)

∠MAN = 110^o

Major arc MN subtend reflex ∠MON at the

Centre and ∠MAN at the remaining part of

the choice.

Reflex ∠MAN at the remaining part of the circle

Reflex ∠MON = 2 ∠MAN = 2 × 110^o =220^o