An angle is equal to one-third of its supplement. Find the numerical measure of the angle (in degrees).

Introduction / Context:
Supplementary angles sum to 180°. If one angle is a fixed fraction of its supplement, we can set up a linear equation to compute the exact measure.

Given Data / Assumptions:

• Let the required angle be x°.
• Its supplement is 180 − x.
• Given: x = (1/3) * (180 − x).

Concept / Approach:
Model the verbal statement as an equation and solve for x with simple algebra.

Step-by-Step Solution:

Verification / Alternative check:
The supplement is 135°. One-third of 135° is 45°, which matches x, so the condition holds.

Why Other Options Are Wrong:

• 40°, 50°, 55° do not satisfy x = (1/3)(180 − x).

Common Pitfalls:
Using complement (sum 90°) instead of supplement (sum 180°), or incorrectly solving the proportion.

Final Answer:
45°