ABCD is a quadrilateral. Three of the angles of ABCD measure 100°, 87, and 106°, respectively. Find the measure of the missing angle
A. 67
B. 74°
C. 80
D. 870

A

Step-by-step explanation:

The angles in a quadrilateral add up to 360 degrees.

100 + 87 + 106= 293

360 - 293 = 67

The missing angle is 67°.  (A)

EVERY quadrilateral has four inside angles that add up to 360°.  It doesn't matter whether the quadrilateral is the size of a strep bacterium or the size of a galaxy. The inside angles always add up to 360°. It's a quadrilateral thing.

In this question, the first three angles add up to (100°+87°+106°) = 293°.

From there, it takes 67° more to get to 360°, so that's what the fourth angle has to be.