Exercises: Measuring and Sketching Angles Using a Protractor
Work through each section in order. Before you trust a scale reading, always classify
the angle by eye first -- acute, right, or obtuse -- and check that your reading agrees.
Recall / Warm-Up
These problems review skills from earlier lessons that this lesson depends on.
A protractor is shaped like a half circle. A full circle is 360 degrees. How many degrees does the protractor's half circle cover?
An angle looks clearly obtuse -- wider than a right angle. Which of these could be its measure?
35 degrees
90 degrees
145 degrees
200 degrees
When reading a measurement from a numbered scale (like a ruler), you should...
Read the number written at the exact mark where the measurement lands.
Count how many tick lines you cross, starting from 1.
Always assume the scale starts at 10.
Ignore the numbers and estimate.
Fluency Practice
A protractor's baseline lies along one ray of an angle. That ray sits at 0 degrees on the inner scale and 180 degrees on the outer scale. The second ray crosses the inner scale at 55 and the outer scale at 125. What is the angle's measure?
55 degrees
125 degrees
180 degrees
0 degrees
A protractor's baseline lies along one ray of an angle. That ray sits at 0 degrees on the outer scale this time. The second ray crosses the inner scale at 40 and the outer scale at 140. What is the angle's measure?
140 degrees
40 degrees
180 degrees
100 degrees
An angle's baseline ray reads 0 degrees on the inner scale. The second ray crosses the inner scale at 75 degrees. What is the angle's measure?
An angle's baseline ray reads 0 degrees on the inner scale. The second ray crosses the inner scale at 150 and the outer scale at 30. The angle looks obtuse when you look at it. Which reading is correct?
150 degrees
30 degrees
Both are equally likely to be correct.
Neither reading can be trusted.
You are sketching a 65-degree angle. After drawing the first ray and aligning the protractor's baseline along it, on which scale value (using the scale that reads 0 along the baseline) do you mark your dot?
You are sketching a 140-degree angle. Before marking the dot, should it fall before or after the 90-degree mark on the scale?
After the 90-degree mark, since 140 degrees is obtuse (greater than 90 degrees).
Before the 90-degree mark, since 140 degrees is a small angle.
Exactly at the 90-degree mark.
It does not matter where the dot falls.
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