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The ratio of the exterior angle to the interior angle of ...

The ratio of the exterior angle to the interior angle of a regular polygon is 1:11. How many sides has the polygon?

A.

30

B.

24

C.

18

D.

12

Correct answer is B

Let a represent an interior angle; e represent an exterior angle. A section of the polygon is down in the diagram.

ea = l11 given

a = 11e

a + e = 180o(angles on a straight line)

11e + e = 180o

12e = 180o

e = 180o12

= 15o

Hence, number of sides

= \frac{360^o}{\tect{size of one exterior angle}

= 360o14o

= 24