Arithmetic Grade Five

Lesson One hundred and fifty-one: Interior Angles of Triangles

Since we know that the sum of the interior angles of a triangle is always 180 degrees, we can always figure out the size of the third angle providing that we know the size of the other two.
  1. 34 degrees
  2. 108 degrees
  3. 38 degrees
Find the missing angle:
  1. 32 degrees
  2. 95 degrees

The missing angle will equal: 

   180 - 32 - 95 =
Solving this problem will yield 53 degrees as the size of the missing angle.
Find the missing angle:
  1. 26 degrees
  2. 96 degrees
The solution: 

   180 - 26 - 96 = 58 degrees

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