SSC CHSL Model Paper 12

The vertically opposite angles of a rhombus are equal. And a diagonal bisects the vertex angle.
Let the angle CDB be x.
So, ∠ADB = x and ∠ABC = ∠ADC = 2x
∠DCB = 70
Now, 70 + 70 + 2x + 2x = 360
⇒ 140 + 4x = 360
⇒ 4x = 220
⇒ x = 55