If four exterior angles of a convex polygon measure 50 degrees, find the measure of the fifth exterior angle.
-20 degrees
-50 degrees
-130 degrees
-160 degrees
i just want to understand how to do this : /

The exterior angles of any polygon add up to 360.  (A square has four sides, each has an exterior angle of 90 - an octagon has eight sides, each side has an exterior angle of 45 (8 x 45 = 360))

You know that four of the five sides of your polygon has exterior angles of 50, making a total of 200 (4 x 50).  The final angle needs to add up to 360 so is 360 - 200 = 160