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Geometry Difficulty 4.4 AIME Find the answer Italy

Problem:

A polygon is called convex if all its interior angles have measure strictly less than 180180^{\circ}. What is the maximum number of angles of measure less than 150150^{\circ} that a convex polygon with 2016 sides can have?

Pick one

Solution

Solution:

The answer is (A). Consider a convex polygon with 2016 sides, and suppose it has exactly aa angles of measure less than 150150^{\circ}; the sum of its interior angles equals (20162)180(2016 - 2) \cdot 180^{\circ}. At the same time, since each of the remaining 2016a2016 - a angles has measure less than 180180^{\circ}, this sum is strictly less than a150+(2016a)180a \cdot 150^{\circ} + (2016 - a) \cdot 180^{\circ}. We thus obtain the inequality
2014180<a150+(2016a)180, 2014 \cdot 180^{\circ} < a \cdot 150^{\circ} + (2016 - a) \cdot 180^{\circ},
that is, a30<360a \cdot 30^{\circ} < 360^{\circ}, from which a<12a < 12.
On the other hand, it is not difficult to see that there exists a polygon with 11 angles of measure 149149^{\circ} and 2005 angles of measure 12005(201418011149)\frac{1}{2005}\left(2014 \cdot 180^{\circ} - 11 \cdot 149^{\circ}\right).

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Source: MathNet, licensed CC-BY-4.0. Statement translated into English from it; metadata (topic, difficulty) added by this project.