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Angles and Triangles Worksheet for Maths Olympiad

Maths Olympiad topic 21: Angles and triangles · Set 665 · 40 questions
TalentJR

How to solve it (180 is the magic number): The three angles of a triangle add up to 180°. An exterior angle equals the sum of the two interior angles opposite it. An isosceles triangle has two equal angles, opposite its two equal sides. Angles on a straight line add up to 180°; vertically opposite angles are equal.

NameDateTime takenScore ___ / 40
  1. 1.Two straight lines cross. One of the angles is 35°. What is the angle next to it on the same straight line? (a) 35° (b) 325° (c) 145° (d) 55°
  2. 2.In an isosceles triangle, the two equal angles are 70° each. What is the third angle? (a) 20° (b) 40° (c) 110° (d) 70°
  3. 3.Two angles of a triangle are 80° and 85°. What is the third angle? (a) 95° (b) 100° (c) 165° (d) 15°
  4. 4.Two angles of a triangle are 70° and 85°. What is the third angle? (a) 110° (b) 155° (c) 95° (d) 25°
  5. 5.Two angles of a triangle are 30° and 115°. What is the third angle? (a) 145° (b) 65° (c) 35° (d) 150°
  6. 6.Two straight lines cross. One of the angles is 50°. What is the angle next to it on the same straight line? (a) 310° (b) 40° (c) 50° (d) 130°
  7. 7.Two angles of a triangle are 50° and 90°. What is the third angle? (a) 40° (b) 90° (c) 130° (d) 140°
  8. 8.Two straight lines cross. Two vertically opposite angles add up to 160°. What is each of the other two angles? (a) 200° (b) 20° (c) 100° (d) 80°
  9. 9.Two straight lines cross. Two vertically opposite angles add up to 210°. What is each of the other two angles? (a) 105° (b) 150° (c) 75° (d) 76°
  10. 10.Two angles of a triangle are 80° and 40°. What is the exterior angle at the third corner? (a) 140° (b) 60° (c) 100° (d) 120°
  11. 11.Two angles of a triangle are 60° and 55°. What is the third angle? (a) 115° (b) 120° (c) 65° (d) 125°
  12. 12.Two angles of a triangle are 50° and 85°. What is the third angle? (a) 130° (b) 95° (c) 45° (d) 135°
  13. 13.Two angles of a triangle are 20° and 30°. What is the third angle? (a) 160° (b) 150° (c) 50° (d) 130°
  14. 14.Two angles of a triangle are 30° and 60°. What is the exterior angle at the third corner? (a) 150° (b) 270° (c) 120° (d) 90°
  15. 15.Two angles of a triangle are 20° and 115°. What is the exterior angle at the third corner? (a) 65° (b) 135° (c) 160° (d) 45°
  16. 16.Two straight lines cross. Two vertically opposite angles add up to 100°. What is each of the other two angles? (a) 130° (b) 50° (c) 80° (d) 260°
  17. 17.Two angles of a triangle are 25° and 35°. What is the exterior angle at the third corner? (a) 145° (b) 60° (c) 155° (d) 120°
  18. 18.In an isosceles triangle, the two equal angles are 55° each. What is the third angle? (a) 70° (b) 55° (c) 35° (d) 125°
  19. 19.Two straight lines cross. Two vertically opposite angles add up to 110°. What is each of the other two angles? (a) 250° (b) 70° (c) 125° (d) 55°
  20. 20.Two angles of a triangle are 65° and 55°. What is the exterior angle at the third corner? (a) 60° (b) 115° (c) 120° (d) 125°
  21. 21.In an isosceles triangle, the two equal angles are 40° each. What is the third angle? (a) 140° (b) 40° (c) 100° (d) 50°
  22. 22.Two straight lines cross. Two vertically opposite angles add up to 90°. What is each of the other two angles? (a) 45° (b) 135° (c) 270° (d) 90°
  23. 23.Two angles of a triangle are 45° and 105°. What is the exterior angle at the third corner? (a) 150° (b) 135° (c) 30° (d) 75°
  24. 24.Two angles of a triangle are 75° and 35°. What is the third angle? (a) 110° (b) 70° (c) 145° (d) 105°
  25. 25.Two angles of a triangle are 45° and 90°. What is the third angle? (a) 90° (b) 135° (c) 45° (d) 225°
  26. 26.Two angles of a triangle are 30° and 35°. What is the exterior angle at the third corner? (a) 145° (b) 150° (c) 115° (d) 65°
  27. 27.Two angles of a triangle are 50° and 45°. What is the exterior angle at the third corner? (a) 130° (b) 85° (c) 135° (d) 95°
  28. 28.Two angles of a triangle are 35° and 100°. What is the exterior angle at the third corner? (a) 80° (b) 145° (c) 135° (d) 45°
  29. 29.Two straight lines cross. One of the angles is 145°. What is the angle next to it on the same straight line? (a) 145° (b) 35° (c) 215° (d) 36°
  30. 30.Two angles of a triangle are 70° and 60°. What is the third angle? (a) 120° (b) 130° (c) 50° (d) 110°
  31. 31.Two angles of a triangle are 25° and 90°. What is the third angle? (a) 90° (b) 115° (c) 155° (d) 65°
  32. 32.Two straight lines cross. Two vertically opposite angles add up to 220°. What is each of the other two angles? (a) 140° (b) 70° (c) 110° (d) 71°
  33. 33.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles? (a) 55° (b) 20° (c) 110° (d) 70°
  34. 34.Two angles of a triangle are 40° and 80°. What is the third angle? (a) 60° (b) 120° (c) 140° (d) 100°
  35. 35.Two angles of a triangle are 60° and 40°. What is the exterior angle at the third corner? (a) 100° (b) 80° (c) 120° (d) 140°
  36. 36.Two angles of a triangle are 70° and 45°. What is the third angle? (a) 110° (b) 65° (c) 135° (d) 115°
  37. 37.Two angles of a triangle are 45° and 45°. What is the third angle? (a) 270° (b) 135° (c) 90° (d) 91°
  38. 38.In an isosceles triangle, the two equal angles are 65° each. What is the third angle? (a) 115° (b) 25° (c) 50° (d) 65°
  39. 39.Two angles of a triangle are 50° and 95°. What is the third angle? (a) 145° (b) 35° (c) 130° (d) 85°
  40. 40.Two straight lines cross. One of the angles is 135°. What is the angle next to it on the same straight line? (a) 46° (b) 135° (c) 45° (d) 225°

Answer key

  1. 145°
  2. 40°
  3. 15°
  4. 25°
  5. 35°
  6. 130°
  7. 40°
  8. 100°
  9. 75°
  10. 120°
  11. 65°
  12. 45°
  13. 130°
  14. 90°
  15. 135°
  16. 130°
  17. 60°
  18. 70°
  19. 125°
  20. 120°
  21. 100°
  22. 135°
  23. 150°
  24. 70°
  25. 45°
  26. 65°
  27. 95°
  28. 135°
  29. 35°
  30. 50°
  31. 65°
  32. 70°
  33. 55°
  34. 60°
  35. 100°
  36. 65°
  37. 90°
  38. 50°
  39. 35°
  40. 45°

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