One interior angle of a convex polygon (a convex polygon is a polygon where all anglesare less than 180 degrees) is 120 degrees. All the other angles are 130 degrees. How many sides does the polygon have?
120 + 130x = 180 * (x+1-2)
120 + 130x = 180x - 180
300 = 50x
x = 6
You get that x = 6, but there is still one angle that equals 120, so you have a 7 sided polygon.