Angles and Measurement — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. When reading a protractor, always start counting from 0 degrees.
You line up one ray of the angle with the 0° mark on the protractor so every degree you count is accurate from that starting point.
2. An angle slightly larger than a right angle, say 95°, is classified as obtuse.
Any angle that measures more than 90° but less than 180° is obtuse, so 95° fits squarely in that category.
3. If a protractor shows 130° on the outer scale, the inner scale reads 50 degrees.
A protractor's two scales always add up to 180°, so when the outer scale reads 130°, the inner scale shows 180° minus 130° = 50°.
4. The hands of a clock at 9:00 form a right angle measuring 90°.
At 9:00 the minute hand points to 12 and the hour hand to 9, which are exactly 3 hours apart, forming a 90° right angle.
5. An angle that measures exactly 0° means the two rays overlap.
When two rays sit right on top of each other with no opening between them, the angle between them is 0°, so they overlap completely.
6. The supplement of a 45° angle is 135 degrees.
Supplementary angles sum to 180°, so 180° minus 45° equals 135°.
7. An angle of 91° is obtuse because it is just over 90°.
At 91° the angle is just barely past a right angle, placing it in the obtuse range (between 90° and 180°).
8. The complement of a 60° angle is 30 degrees.
Complementary angles add up to 90°, so 90° minus 60° leaves 30° for the complement.
9. A clock hand moving from 12 to 3 sweeps 90 degrees.
The numbers 12 to 3 cover one quarter of the clock face, and one quarter of 360° is 90°.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Clock at 12:00
→ 0°
30°
Clock at 3:00
→ 90°
90°
Clock at 6:00
→ 180°
180°
Clock at 1:00
→ 30°
0°
Correct matches: Clock at 12:00 → 0°; Clock at 3:00 → 90°; Clock at 6:00 → 180°; Clock at 1:00 → 30°.