Geometry

Question Analysis:
This question involves deductive reasoning about the angles of a triangle.
The main focus is on applying the Triangle Angle Sum Theorem.

Key Concept Explanation:
The Triangle Angle Sum Theorem states that the sum of the interior angles of a triangle is 180°.

Step-by-Step Solution:
Add the two given angles: 30° + 60° = 90°.
Subtract the sum from 180°: 180° - 90° = 90°.
Deduce that the third angle is 90°.

Common Mistakes: