# Two Angles of a Polygon Are Right Angles and the Remaining Are 120° Each. Find the Number of Sides in It. - Mathematics

Sum

Two angles of a polygon are right angles and the remaining are 120° each. Find the number of sides in it.

#### Solution

Let the number of sides = n

Sum of interior angles = (n - 2) × 180°

= 180n - 360°

Sum of 2 right angles = 2 × 90° = 180°

∴ Sum of other angles = 180n - 360° - 180°

= 180n - 540°

No.of vertices at which these angles are formed = n - 2

∴ Each interior angle = (180"n" - 540)/("n" - 2)

∴ (180 "n" - 540)/("n" - 2) = 120°

180n - 540 = 120n - 240

180n - 120n = - 240 + 540

60n = 300

n = 300/60

n = 5

Concept: Sum of Angles of a Polynomial
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#### APPEARS IN

Selina Concise Mathematics Class 8 ICSE
Chapter 16 Understanding Shapes
Exercise 16 (A) | Q 11 | Page 181