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Grade 4 · lesson 2 of 4

Read a Protractor from the Starting Ray

Locate the stated zero-aligned scale and read its marked ray value.

About 20 minutes, plus any extended practice

Download the grade pack

Supplied materials

  • Paper and a pencil; drawing and spoken explanations are welcome. An adult may read directions and options aloud.
  • Supplied worked-case record: The starting ray is aligned with the scale that reads zero on the right.
  • All quantities and shape descriptions are supplied in the worked example and questions; no purchase or personal information is needed.

Learn the idea

Many protractors have two scales running in opposite directions. Use the scale whose zero lies on the starting ray. Reading the other scale can give a supplementary angle rather than the intended one. This paper exercise supplies both readings so no physical tool is required.

Locate the stated zero-aligned scale and read its marked ray value. Check whether the described angle is acute or obtuse as a reasonableness test. The other scale is not automatically correct just because its numeral is larger.

Choose the scale with zero on the starting ray. A two-scale protractor does not mean both numbers measure the same chosen turn. Sketch the starting ray and label which supplied scale begins at zero there.

  1. Sketch the starting ray and label which supplied scale begins at zero there.
  2. Follow the worked example. Point to each number or shape feature and say what it tells you.
  3. Locate the stated zero-aligned scale and read its marked ray value.
  4. Try the question and then the three practice questions. Check your answers and explain any change you make.
Worked example

See the method in action

The starting ray is aligned with the scale that reads zero on the right. The ending ray is marked 40 on that scale and 140 on the other. The intended measure is 40°. A turn less than a right angle supports forty rather than one hundred forty. Choose the scale with zero on the starting ray. A two-scale protractor does not mean both numbers measure the same chosen turn. Sketch the starting ray and label which supplied scale begins at zero there.

Your turn

Check your reasoning

Your answer is temporary and is not saved to an account. Download your current answer before leaving or reloading. Written work on paper or in another app stays in your own file.

Helpful tips
  • Choose the scale with zero on the starting ray.
  • A two-scale protractor does not mean both numbers measure the same chosen turn.
The starting ray aligns with Scale A’s zero. At the ending ray, A reads 30° and B reads 150°. What angle is measured?

Feedback appears here after you check. This is practice, not a graded school assessment.

See the answer and explanation

30

Read the scale beginning at zero on the stated starting ray. The result is 30.

Take it further

A zero-aligned scale reads 115° while the opposite scale reads 65°. Expected: 115°.

Nothing here is saved to an account or sent to a teacher. The answer download includes your current choice and any checked feedback. It does not include choices from the separate More practice section. Download that section separately.

More practice: try new cases

Choose an answer for each problem. Explain your method on paper, then use the feedback to decide what to revisit.

More practice: try new cases
1. The starting ray aligns with Scale A’s zero. At the ending ray, A reads 40° and B reads 140°. What angle is measured?
Need a hint?
  • Choose the scale with zero on the starting ray.
  • A two-scale protractor does not mean both numbers measure the same chosen turn.
2. The starting ray aligns with Scale A’s zero. At the ending ray, A reads 50° and B reads 130°. What angle is measured?
Need a hint?
  • Choose the scale with zero on the starting ray.
  • A two-scale protractor does not mean both numbers measure the same chosen turn.
3. The starting ray aligns with Scale A’s zero. At the ending ray, A reads 60° and B reads 120°. What angle is measured?
Need a hint?
  • Choose the scale with zero on the starting ray.
  • A two-scale protractor does not mean both numbers measure the same chosen turn.

Your choices are temporary. Feedback appears after you check all the answers.

Nothing here is saved to an account or sent to a teacher. Keep your own notes or download them before leaving. The score describes these questions; it does not certify subject mastery.

Check the subject sources

These LifeStarter passages, scenarios and exercises are authored for this Academy with AI assistance and review. External resources keep their publishers’ terms. A grade label suggests a starting level; it does not establish alignment with your school’s complete requirements.