Arithmetic Grade Six

Lesson One Hundred Forty-five: Interior Angles of Quadrilaterals

Since we know that the sum of the interior angles of a quadrilateral is always 360 degrees, we can always figure out the size of the fourth angle providing that we know the size of the other three.
  1. 103 degrees
  2. 75 degrees
  3. 77 degrees
  4. 105 degrees
Find the missing angle:
  1. 106 degrees
  2. 93 degrees
  3. 73 degrees

The missing angle will equal: 

   360 - 106 - 93 - 73 =
Solving this problem will yield 88 degrees as the size of the missing angle.
Find the missing angle:
  1. 103 degrees
  2. 100 degrees
  3. 76 degrees
The solution: 

   360 - 103 - 100 - 76 = 81 degrees

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