16Hit1600
Geometry and TrigonometryEasyFourth angle of a quadrilateral with two right angles

Geometry and Trigonometry practice question

A quadrilateral has two right angles, and a third angle measures 120°. What is the measure, in degrees, of the fourth angle?

Answer: 60

The four angles add to 360: 360 − 90 − 90 − 120 = 60.

Common wrong answers

If you answered 120
The fourth angle need not equal the third; 90 + 90 + 120 + 120 = 420, too much.
If you answered 150
150 is 360 − 90 − 120, counting only one right angle.
If you answered -30
−30 comes from using 180 as the total; a quadrilateral's angles add to 360.

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