NCERT Exemplar Solutions
Class 6 - Mathematics - Unit 9: Symmetry and Practical Geometry - Multiple Choice Questions

Question 8

Why the correct answer is Protractor

Simple idea: To measure how wide an angle opens, we use a tool that has degree markings (0° to 180° or 0° to 360°). That tool is a protractor.

What each tool does

• Ruler: Measures length in cm/mm. It does not measure angles.
• Protractor: Measures angles in degrees (°). ✔️
• Divider: Has two sharp legs; used to mark equal lengths or transfer distances.
• Compasses: Used to draw circles or arcs.

How to use a protractor (very easy steps)

1. Find the vertex of the angle.

   Example angle: ( angle ABC )

   The vertex is the middle letter: ( B )

2. Place the protractor so that its small center hole (or cross) is exactly on the vertex.

   Center of protractor → ( B )

3. Align the baseline of the protractor with one arm of the angle.

   Baseline (0° line) should lie on one arm through ( B )

4. Choose the correct scale on the protractor.

   If the angle opens to the right, start reading from the 0° on the inner scale.

   If it opens to the left, start from the 0° on the outer scale.

5. Read the number where the other arm of the angle cuts the scale.

   Suppose it meets at ( 60^circ )

   So, ( angle ABC = 60^circ )

Quick checks (to avoid mistakes)

• Is the center of the protractor exactly at the vertex? → ( B )
• Is one arm aligned with the 0° line?
• Did you pick the correct scale (inner or outer) that starts from 0° on your aligned arm?

Conclusion

The instrument that measures an angle is a Protractor.