Which of the following correctly states the sum of the interior angles in a triangle?

• A. The sum is 560 degrees.
• B. The sum is 180 degrees.
• C. The sum is 360 degrees.
• D. The sum is 90 degrees.

Answer: (B)

The sum of the interior angles in a triangle is 180 degrees. This is true for any triangle, whether it’s acute, obtuse, or right-angled. A simple way to see it is to draw a line parallel to one side of the triangle through the opposite vertex. The two angles at the base become corresponding angles with the other two interior angles, so all three interior angles lie on a straight line and add up to 180 degrees. Equivalently, the general rule for any polygon with n sides gives (n−2)×180 degrees; for a triangle (3−2)×180 = 180. The other options don’t fit because 360 relates to quadrilaterals or full turns, 90 is just a single right angle, and 560 exceeds any possible sum for a triangle.