If a triangle has angles 35° and 65°, what is the measure of the third angle?

If a triangle has angles 35° and 65°, what is the measure of the third angle?

• A. 80
• B. 75
• C. 85
• D. 70

Answer: (A)

In any triangle, the interior angles add up to 180 degrees. Add the two given angles: 35° + 65° = 100°. Subtract from 180° to find the third angle: 180° − 100° = 80°. So the third angle is 80 degrees. This also checks since 35° + 65° + 80° = 180°. Other possible angles would not bring the total to 180°.

In any triangle, the interior angles add up to 180 degrees. Add the two given angles: 35° + 65° = 100°. Subtract from 180° to find the third angle: 180° − 100° = 80°. So the third angle is 80 degrees. This also checks since 35° + 65° + 80° = 180°. Other possible angles would not bring the total to 180°.