Drafting instruments — divisions on a half-moon (semicircular) protractor A standard semicircular protractor is graduated into how many degrees?

Introduction / Context:Protractors are used to measure and construct angles in drafting and geometry. The common “half-moon” or semicircular protractor covers a half-circle, while full-circle versions exist for specialized work. Knowing the graduations helps avoid measurement mistakes when transferring angles to drawings.

Given Data / Assumptions:

• A semicircle spans half of a full circle.
• A full circle contains 360 degrees.

Concept / Approach:Since a full circle is 360 degrees, a semicircle necessarily spans 180 degrees. Therefore, a standard semicircular protractor is graduated from 0 to 180 degrees (often with dual scales running opposite directions for inside/outside measurements).

Step-by-Step Solution:

Verification / Alternative check:Inspection of standard school or drafting protractors shows ends labeled 0 and 180, with midpoints at 90 degrees.

Why Other Options Are Wrong:

• 360 and 270: represent full circle and three-quarters of a circle, not a semicircle.
• 310 and 90: not standard for half-circle graduation counts; 90 is a quarter circle.

Common Pitfalls:

• Reading the wrong scale direction; many protractors have mirrored numbering to measure from either edge.

Final Answer:180