Question

What is the measure of the fourth angle of a quadrilateral if the other three angles measure 70° , 90 °,120°?

Answer 1

Sum of all the angles of a quadrilateral is 360°
let the fourth angle be x 
⇒ 70°+90°+120°+x=360°
⇒280°+x=360°
⇒x=360°-280°
⇒x=80°
⇒So the fourth angle is 80°

Answer 2

Heya,

Let the 4th angle be x

Sum of the 4 angles of a quadrilateral = 360°------(1)

Given,

3 angle measures are 70° , 90 °,120°

So,

70+90+120+x = 360°(from 1)

280+x =360°

x = 80°

Therefore the 4th angle = 80°

Hope it helps u...........