Measuring Angles With a Protractor Students are asked to use a protractor to determine the measure of four angles.

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1 This is a resource from CPALMS ( where all educators go for bright ideas! Resource ID#: Primary Type: Formative Assessment Measuring Angles With a Protractor Students are asked to use a protractor to determine the measure of four angles. Subject(s): Mathematics Grade Level(s): 4 Intended Audience: Educators Freely Available: Yes Keywords: MFAS, angle, protractor, degrees, measure, ray, vertex, decompose Instructional Component Type(s): Formative Assessment Resource Collection: MFAS Formative Assessments ATTACHMENTS MFAS_MeasuringAnglesWithAProtractorWorksheet.docx FORMATIVE ASSESSMENT TASK Instructions for Implementing the Task Note: This task may be implemented individually, in small groups, or in a whole-group setting. If the task is given in a whole-group setting, the teacher should ask each student to explain his or her thinking and strategy. 1. The teacher provides the student with a protractor (either a 360 degree or 180 degree) and the Measuring Angles With a Protractor worksheet and reads the directions aloud. 2. The teacher provides the student with adequate time to complete the worksheet and then asks the student to explain how he or she used the protractor to determine the measure of each angle. Since protractors are not exact instruments, students should be given a margin of error in construction. TASK RUBRIC Getting Started The student does not know how to correctly use a protractor to measure angles. The student is unable to use a protractor to measure the angles. The student: Uses the centimeter ruler or inch ruler instead of the baseline when measuring the angles. Measures the length of each ray and sums the lengths. page 1 of 5

2 Measures the distance between the two rays using the ruler on the protractor. Does not correctly line up the angle to be measured on the protractor. Can you show me how you measured the angle with the protractor? Where should one of the rays be lined up? What do you do with the other ray? Where does the vertex of the protractor go on the angle? How do you know which scale to use on the protractor when you are measuring or drawing angles? What does a 90 degrees angle look like? What about a 45 degrees angle? How can you use this knowledge to help you decide which numbers you need to read on the protractor? Review or reteach the angle classifications (acute, right, and obtuse) so that the student understands the relative size of angles. Provide instruction on how use a protractor to measure and draw angles of a given measure. Consider using a 360 degree protractor initially, if available. Then transition to using a conventional 180 degree protractor to measure and draw angles. Use a circular protractor to explain that a one-degree angle is of a full turn. Relate the student s understanding of one degree turns to using a protractor to determine an angle s measure. Emphasize and explore benchmark angles. Once the student is proficient with measuring angles using a protractor, have the student draw angles of a specified measure. Consider using the MFAS task Lawn Sprinkler (4.MD.3.5). Consider using the MFAS task Using a Protractor to Draw Angles (4.MD.3.6) to assess a student s understanding of drawing angles using a protractor. Moving Forward The student gives the measure of the supplementary angle. The student correctly positions the protractor on the angle but confuses the inner and outer scales on the protractor and gives the measure of the supplementary angle as page 2 of 5

3 the answer. The student is unable to determine the measure of the reflex angle. Is angle C acute or obtuse? What do you know about acute angles? Can an acute angle measure 130 degrees? What does a 90 degree angle look like? What about a 45 degree angle? How can you use this knowledge to help you decide which numbers you need to use on the protractor? How do you know which scale to use on the protractor when you are measuring or drawing angles? Is the angle you are measuring acute or obtuse? Does your answer make sense based on the type of angle? Review acute and obtuse angles. Encourage the student to use this information to determine if the angle shown is acute or obtuse and if that matches the angle measure provided. Review the procedure for measuring angles using a protractor. Explain how to determine which scale to use in a given situation. Almost There The student is not able to use a protractor to determine the measure of a reflex angle. The student correctly measures the three angles less than 180 degrees but is unable to measure the 225 degree angle. The student knows the angle is greater than 180 degrees but is unable to determine how to measure the angle using a protractor. How many degrees are in a circle? How can this help you find the measure of the reflex angle? What is one thing you can tell me about the reflex angle? Is the angle greater than 90 degrees? Is it greater than 180 degrees? If the angle is greater than 180 degrees, what can you do to determine the measure of the angle? Can angle measures be additive? Can you decompose this angle into two smaller angles? How would you do that? Ensure that the student understands that angle measure is additive. Consider using the MFAS task Using Known Angles (4.MD.3.7) to determine if the student understands the additive nature of the angle measure. Provide instruction for the student on adjacent angles: Model how to add the measures of two adjacent angles to find the measure of the larger angle formed by their outer rays. Start with angles that measure less than 180 degrees. Model how to decompose reflex angles into two adjacent angles whose measures are less than 180 degrees. Have the student measure each of the smaller adjacent angles and sum their measures to determine the measure of the reflex angle. Provide opportunities for the student to practice decomposing angles including angles less than 180 degrees into two adjacent angles. Then have the student determine the measure of each smaller angle to find the measure of the composed angle. Provide opportunities for the student to work with other students to find the measure of angles and to understand that angle measure can be additive. Have each student draw an angle of a specified measure and then exchange angles. Each student then decomposes the angle into two angles, finds the measure of each angle, and then adds the measures to determine the measure of the original angle. The students can then compare how they determined the angle measure. Got It The student provides complete and correct responses to all components of the task. The student correctly measures angle A as 225 degrees, angle B as 90 degrees, angle C as 50 degrees, and angle D as 150 degrees. The student finds the measurement of reflex angle A by: page 3 of 5

4 Decomposing the angle into adjacent angles of 180 and 45 degrees and summing the two angles. Finding the measurement of the other side of the angle and then subtracting it from 360 degrees. The student understands that a circle has 360 one-degree turns and says if I subtract the other portion of this circle then I can find the measurement of the reflex angle A. How many right angles are in a circle? What are complementary angles? What are supplementary angles? Can you bisect the obtuse angle and measure each of those? What do you know will be certain about the sum of the two new angles? Can you draw another angle adjacent to the 50 degree angle that will make the sum of the two angles 90 degrees? Note: This could also be phrased, Can you draw an angle that is both complementary and adjacent to the 50 degree angle? Introduce the concept of an angle bisector. Ask the student to determine how to use a protractor to draw the bisector of an angle. Ask the student to draw angles that are complementary and adjacent or supplementary and adjacent to the given angles. Consider using MFAS task Town of Happyville (4.MD.3.6) to assess the student s understanding of applying angle measurements in a real world situation to draw specified angle measurements. ACCOMMODATIONS & RECOMMENDATIONS Special Materials Needed: Measuring Angles With a Protractor worksheet Protractor SOURCE AND ACCESS INFORMATION Contributed by: MFAS FCRSTEM Name of Author/Source: MFAS FCRSTEM District/Organization of Contributor(s): Okaloosa Is this Resource freely Available? Yes Access Privileges: Public License: CPALMS License - no distribution - non commercial Related Standards Name Description page 4 of 5

5 MAFS.4.MD.3.6: Measure angles in whole-number degrees using a protractor. Sketch angles of specified measure. page 5 of 5