Each interior angle of a regular polygon is 18° more than

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Each interior angle of a regular polygon is 18° more than eight times an exterior angle. The number of sides of the polygon is

Let the number of sides of the regular polygon be n, then

∴		2n - 4		× 90
		n

= 8 ×	4 × 90°	+ 18
	n

⇒		2n - 4		× 5 =	160	+ 1
		n			n

⇒ 10 = n – 20 = 160 + n
⇒ 10n – n = 180
⇒ 9n = 180
⇒ n = 20