If the sum of interior angles of a polygon is $1440^{\circ}$, the number of sides is:

If the sum of interior angles of a polygon is $1440^{\circ}$, the number of sides is:
  1. $8$
  2. $9$
  3. $10$
  4. $12$

Solution

$(n-2) \times 180 = 1440 \Rightarrow n-2 = 8 \Rightarrow n = 10$.

Asked in: IMO

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