A triangle has angles 40° and 65°. What is the third angle?

A triangle has angles 40° and 65°. What is the third angle?

• A. 75°
• B. 85°
• C. 55°
• D. 65°

Answer: (A)

In any triangle, the interior angles add up to 180 degrees. So with two angles 40 degrees and 65 degrees, add them to get 105 degrees. The remaining angle is 180 minus 105, which equals 75 degrees. The other options don’t fit because adding them to 40 and 65 would not reach the total of 180 degrees (for example, 40 + 65 + 85 = 190; 40 + 65 + 55 = 160; 40 + 65 + 65 = 170).

In any triangle, the interior angles add up to 180 degrees. So with two angles 40 degrees and 65 degrees, add them to get 105 degrees. The remaining angle is 180 minus 105, which equals 75 degrees. The other options don’t fit because adding them to 40 and 65 would not reach the total of 180 degrees (for example, 40 + 65 + 85 = 190; 40 + 65 + 55 = 160; 40 + 65 + 65 = 170).