If the ratio of an external angle and an internal angle of a regular polygon is 2:15, how many sides does this polygon has?
Given, the ratio of an external angle and on internal angle of a regular polygon is 2:15. ⇒ 360/[(2n - 4) * 90] = 2/15 ⇒ 4n - 8 = 60 ⇒ n = 17
