Angles and Measurement — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. The complement of a 35° angle is 55 degrees.
Complementary angles add up to 90°, so subtract 35° from 90° to get 55°.
2. The supplement of a 100° angle is 80 degrees.
Supplementary angles add up to 180°, so 180° minus 100° gives 80°.
3. If two supplementary angles are equal, each measures 90 degrees.
Two equal supplementary angles must split 180° evenly, so each one measures 180° divided by 2, which is 90°.
4. An angle and its complement always add up to 90 degrees.
By definition, complementary angles are two angles whose measures combine to exactly 90°.
5. A protractor has 180 degree marks from 0° to 180°.
A standard protractor is a half-circle, so it marks every degree from 0° up to 180°, giving it 180 degree marks.
6. The supplement of a 25° angle is 155 degrees.
Supplementary angles sum to 180°, so 180° minus 25° equals 155°.
7. If two complementary angles are equal, each measures 45 degrees.
Two equal complementary angles share 90° equally, so each one is 90° divided by 2, which is 45°.
8. An angle of 89° is classified as acute because it is less than 90°.
Since 89° is just below 90°, it falls in the acute range, which includes every angle greater than 0° and less than 90°.
9. The complement of a 12° angle is 78 degrees.
Complementary angles total 90°, so subtract 12° from 90° to find the complement: 78°.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Supplement of 40°
→ 140°
90°
Complement of 55°
→ 35°
80°
Supplement of 90°
→ 90°
140°
Complement of 10°
→ 80°
35°
Correct matches: Supplement of 40° → 140°; Complement of 55° → 35°; Supplement of 90° → 90°; Complement of 10° → 80°.