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If the difference between the interior and exterior angles of a regular polygon is 144° then what is the number of sides of the polygon?
Question

If the difference between the interior and exterior angles of a regular polygon is 144° then what is the number of sides of the polygon?

A.

12

B.

16

C.

18

D.

20

Correct option is D

Given:

Difference between the interior and exterior angles of a regular polygon = 144º

Concept Used:

For a regular polygon with n sides:

  • Interior angle = (n-2) × 180º / n
  • Exterior angle = 360º / n

Solution:

144 = [(n-2) × 180 / n] - (360 / n)

=> 144 = (180n - 360 - 360) / n

=> 144 = (180n - 720) / n

=> 144n = 180n - 720

=> 180n - 144n = 720

=> 36n = 720

=> n = 720 / 36

=> n = 20

Hence, the number of sides of the polygon is 20.

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