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Primary 4 Mathematics · Chapter 7 · Answers and explanations

Lesson 7.4: Drawing Angles (answers)

Section A · Multiple choice 4 marks

1. Mei wants to draw ∠ABC = 50°. Where should the centre of the protractor be placed?1 mark

(A) on B(B) on A(C) on C(D) on the middle of AB
Answer: (A) on BThe vertex is B (the middle letter). Put the centre of the protractor on the vertex B, with the baseline along arm BA.

2. Which is the best estimate of the size of this angle?1 mark

about 120°
(A) 30°(B) 120°(C) 60°(D) 170°
Answer: (B) 120°It is wider than a square corner (90°) but not nearly a straight line (180°), so about 120° is the best estimate.

3. Sara wants to draw an angle of 130°. Her angle should be1 mark

(A) an acute angle(B) a right angle(C) an obtuse angle(D) a straight line
Answer: (C) an obtuse angle130° is more than 90° and less than 180°, so it is an obtuse angle.

4. Mei put the centre of the protractor on B and the baseline along BA. She made a dot at 55 on the inner scale (the red dot). She will join the dot to B. What angle will she draw?1 mark

01801017020160301504014050130601207011080100909010080110701206013050140401503016020170101800ABC∠ABC = 55°
(A) 125°(B) 35°(C) 65°(D) 55°
Answer: (D) 55°The arm BA is on 0 at the left, so Mei is using the inner scale. The dot is at 55, so ∠ABC = 55°. (125° is the number on the outer scale.)

Section B · Write your answer 11 marks

5. Using a ruler and a protractor, draw ∠ABC = 40°. The line BA is drawn for you.1 mark

ABC∠ABC = 40°
Answer: Check: ray BC makes a 40° angle with BA (acute).Put the centre of the protractor on B and the baseline along BA. Start at 0 on the scale and count to 40. Make a dot, then join it to B with a ruler. Label the dot C.

6. Using a ruler and a protractor, draw ∠PQR = 75°. The line QP is drawn for you.1 mark

PQR∠PQR = 75°
Answer: Check: ray QR makes a 75° angle with QP (acute).Put the centre on Q and the baseline along QP. Start at 0 and count to 75. Make a dot, join it to Q and label it R.

7. Using a ruler and a protractor, draw ∠XYZ = 120°. The line YX is drawn for you.1 mark

XYZ∠XYZ = 120°
Answer: Check: ray YZ makes a 120° angle with YX (obtuse).Put the centre on Y and the baseline along YX. YX points to the left, so start at 0 on the inner scale and count to 120. Make a dot, join it to Y and label it Z.

8. Which angle is bigger, X or Y?1 mark

X = 35°Y = 100°
Answer: Angle YAngle Y opens wider than Angle X. Y is 100° and X is 35°.

9. Zara was asked to draw an angle of 80°. She drew the angle below. Is her angle correct? 1 mark

01801017020160301504014050130601207011080100909010080110701206013050140401503016020170101800ABCThe angle is 100°, not 80°
Answer: No; it is 100°One arm is on 0 at the left, so read the inner scale. The other arm is at 100, not 80. Zara used the wrong scale.

10. Using a ruler and a protractor, draw ∠XYZ = 145°. Is it acute, right or obtuse?2 marks

XYZ∠XYZ = 145°
Answer: Check: 145° angle; obtusePut the centre on Y and the baseline along YX. Count to 145 from 0. Join the dot to Y. 145° is more than 90° and less than 180°, so it is an obtuse angle.

11. Tim was asked to draw an angle of 60°. He drew the angle below. Is it correct? How do you know?2 marks

ACBThis angle is 120°
Answer: No; it is 120° (obtuse), but 60° must be acute60° is smaller than a right angle, so it must be an acute angle. Tim's angle is wider than a square corner. He read the wrong scale (120° instead of 60°).

12. Draw ∠AOB = 30°. Then draw ∠BOC = 50° so that it is next to ∠AOB. What is the size of ∠AOC?2 marks

AOBC∠AOC = 30° + 50° = 80°
Answer: 80°Draw OB at 30° from OA. Then draw OC at 50° from OB, which is 30° + 50° = 80° from OA. ∠AOC = 80°.
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