Angles and Angle Measurement — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. An angle of 55° is classified as acute.
55° is less than 90°, so it is an acute angle.
2. If two angles together form a right angle, they add up to 90 degrees.
Complementary angles sum to 90°.
3. An angle of 90° plus an angle of 40° equals 130 degrees.
90 + 40 = 130 degrees.
4. A straight angle minus 65° equals 115 degrees.
180 − 65 = 115 degrees.
5. An angle of 162° is classified as obtuse.
162° is between 90° and 180°, so it is an obtuse angle.
6. Two angles that add up to 90° are called complementary angles.
Complementary angles are a pair that together form a 90° right angle.
7. If one angle in a pair of supplementary angles is 110°, the other is 70 degrees.
Supplementary angles sum to 180°: 180 − 110 = 70°.
8. A quarter turn measures 90 degrees.
A quarter of a full rotation (360°) = 360 ÷ 4 = 90°.
9. If one angle of a straight angle pair is 45°, the other is 135 degrees.
Supplementary angles sum to 180°: 180 − 45 = 135°.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Exactly 90°
→ Right angle
Obtuse angle
Between 90° and 180°
→ Obtuse angle
Acute angle
Exactly 180°
→ Straight angle
Right angle
Less than 90°
→ Acute angle
Straight angle
Exactly 90° → Right angle; Between 90°-180° → Obtuse angle; Exactly 180° → Straight angle; Less than 90° → Acute angle.