Question

four angle of a pentagon are 100 degree, 175 degree, 85 degree and 75 degree. find the fifth angle.

Answer 1

Four angles of a pentagon have measures 30, 60, 120, and 165. Find the measure of the fifth angle. 
-----------
The sum of the angles of any polygon with n sides is
180*(n-2)
A pentagon has 5 sides. 180*(3) = 540º
30 + 60 + 120 + 165 = 385º
The 5th angle is 540 - 385
= 155º 

Answer 2

Sum of all angles of pentagon = (5-2)×180°
=3×180°
=540°
Fifth angle= 540°-(180°+175°+85°+75°)
=540°-515°
=25°