If sum of all interior angles of a regular polygon is 18 right angles. Then, find the number of sides of the polygon.

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answer is A.

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Detailed Solution

Given the sum of all interior angles of a regular polygon is 18 right angles.
Sum of all interior angles is,= 18 ✕ (right angles)

⇒ S u m o f a l l i n t e r i o r a n g l e s = 18 × 90 °

⇒ S u m o f a l l i n t e r i o r a n g l e s = 1620 °

Also, sum of interior angle is

1620 ° = 2 n − 4 × 90 ° ⇒ 1620 ° 90 ° = 2 n − 4 ⇒ 18 = 2 n − 4 ⇒ 2 n = 18 + 4 ⇒ 2 n = 22 ⇒ n = 222 ⇒ n = 11

Therefore, number of side is 11.
Hence, option 1 is correct.

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