If two interior angles measure 85 degrees and 40 degrees, what is the measure of the third angle?

If two interior angles measure 85 degrees and 40 degrees, what is the measure of the third angle?

• A. 125 degrees
• B. 40 degrees
• C. 55 degrees
• D. 90 degrees

Answer: (C)

In a triangle, the interior angles add up to 180 degrees. The two given angles sum to 85 + 40 = 125 degrees, so the remaining angle must make the total 180. That gives 180 − 125 = 55 degrees. So the third angle measures 55 degrees. The other sums would not reach 180, so they aren’t possible for a triangle.

In a triangle, the interior angles add up to 180 degrees. The two given angles sum to 85 + 40 = 125 degrees, so the remaining angle must make the total 180. That gives 180 − 125 = 55 degrees. So the third angle measures 55 degrees. The other sums would not reach 180, so they aren’t possible for a triangle.