The angles of a quadrilateral are in A.P. with a common difference of 10 degrees. Find the smallest angle.
Answer: B
Let the angles be \(a, a+10, a+20, a+30\). The sum of angles in a quadrilateral is 360°. So, \(a + (a+10) + (a+20) + (a+30) = 360 \Rightarrow 4a + 60 = 360 \Rightarrow 4a = 300 \Rightarrow a = 75\). The smallest angle is 75°.