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You are given that the ratio of the interior angle of the regular n-gon to its exterior angle is 10:2, i.e, 5:1.
From the other side, the sum of these angles is 180 degrees, as you should know.
Hence, the exterior angle is = = 30 degrees.
Then the interior angle is 180-30 = 150 degrees, obviously.
From the other side, the sum of the exterior angles of any n-sided convex polygon is 360 degrees.
It gives you an equation
n*30 = 360 degrees
to find the number of sides / (of vertices) of the polygon.
From the equation, you easily find n = = 12.
ANSWER. The given polygon is 12-gon.
From this point, complete the solution on your own.
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