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Angles and Triangles Worksheet for Maths Olympiad

Maths Olympiad topic 21: Angles and triangles · Set 764 · 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 angles of a triangle are 70° and 25°. What is the exterior angle at the third corner? (a) 85° (b) 155° (c) 95° (d) 110°
  2. 2.Two straight lines cross. Two vertically opposite angles add up to 100°. What is each of the other two angles? (a) 50° (b) 130° (c) 80° (d) 260°
  3. 3.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles? (a) 60° (b) 30° (c) 75° (d) 150°
  4. 4.Two straight lines cross. Two vertically opposite angles add up to 50°. What is each of the other two angles? (a) 155° (b) 310° (c) 130° (d) 25°
  5. 5.Two angles of a triangle are 30° and 55°. What is the exterior angle at the third corner? (a) 150° (b) 125° (c) 85° (d) 95°
  6. 6.In an isosceles triangle, the angle between the two equal sides is 90°. What is each of the other two angles? (a) 90° (b) 55° (c) 46° (d) 45°
  7. 7.Two angles of a triangle are 60° and 60°. What is the third angle? (a) 240° (b) 120° (c) 61° (d) 60°
  8. 8.Two angles of a triangle are 75° and 35°. What is the third angle? (a) 70° (b) 105° (c) 110° (d) 145°
  9. 9.Two angles of a triangle are 30° and 120°. What is the exterior angle at the third corner? (a) 30° (b) 210° (c) 150° (d) 60°
  10. 10.Two straight lines cross. Two vertically opposite angles add up to 330°. What is each of the other two angles? (a) 30° (b) 15° (c) 165° (d) 16°
  11. 11.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) 55° (d) 145°
  12. 12.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles? (a) 80° (b) 50° (c) 10° (d) 100°
  13. 13.Two angles of a triangle are 65° and 35°. What is the exterior angle at the third corner? (a) 145° (b) 100° (c) 80° (d) 115°
  14. 14.Two angles of a triangle are 50° and 70°. What is the third angle? (a) 110° (b) 130° (c) 60° (d) 120°
  15. 15.Two angles of a triangle are 65° and 45°. What is the exterior angle at the third corner? (a) 115° (b) 70° (c) 110° (d) 135°
  16. 16.Two straight lines cross. One of the angles is 20°. What is the angle next to it on the same straight line? (a) 20° (b) 160° (c) 340° (d) 70°
  17. 17.Two angles of a triangle are 70° and 85°. What is the third angle? (a) 25° (b) 95° (c) 110° (d) 155°
  18. 18.Two straight lines cross. Two vertically opposite angles add up to 160°. What is each of the other two angles? (a) 20° (b) 100° (c) 200° (d) 80°
  19. 19.In an isosceles triangle, the two equal angles are 25° each. What is the third angle? (a) 130° (b) 155° (c) 25° (d) 65°
  20. 20.Two straight lines cross. One of the angles is 115°. What is the angle next to it on the same straight line? (a) 115° (b) 66° (c) 65° (d) 245°
  21. 21.Two straight lines cross. One of the angles is 95°. What is the angle next to it on the same straight line? (a) 95° (b) 86° (c) 85° (d) 265°
  22. 22.In an isosceles triangle, the two equal angles are 55° each. What is the third angle? (a) 35° (b) 55° (c) 70° (d) 125°
  23. 23.Two angles of a triangle are 35° and 55°. What is the third angle? (a) 145° (b) 270° (c) 90° (d) 125°
  24. 24.Two straight lines cross. One of the angles is 40°. What is the angle next to it on the same straight line? (a) 40° (b) 140° (c) 50° (d) 320°
  25. 25.Two angles of a triangle are 55° and 85°. What is the exterior angle at the third corner? (a) 95° (b) 125° (c) 40° (d) 140°
  26. 26.Two angles of a triangle are 45° and 70°. What is the third angle? (a) 65° (b) 135° (c) 115° (d) 110°
  27. 27.Two angles of a triangle are 75° and 30°. What is the third angle? (a) 105° (b) 75° (c) 255° (d) 150°
  28. 28.Two angles of a triangle are 40° and 45°. What is the exterior angle at the third corner? (a) 140° (b) 135° (c) 95° (d) 85°
  29. 29.Two angles of a triangle are 75° and 60°. What is the exterior angle at the third corner? (a) 45° (b) 105° (c) 135° (d) 120°
  30. 30.Two angles of a triangle are 40° and 90°. What is the third angle? (a) 140° (b) 90° (c) 130° (d) 50°
  31. 31.Two angles of a triangle are 35° and 85°. What is the third angle? (a) 120° (b) 145° (c) 95° (d) 60°
  32. 32.In an isosceles triangle, the two equal angles are 85° each. What is the third angle? (a) 5° (b) 85° (c) 95° (d) 10°
  33. 33.In an isosceles triangle, the two equal angles are 80° each. What is the third angle? (a) 10° (b) 80° (c) 20° (d) 100°
  34. 34.Two straight lines cross. One of the angles is 75°. What is the angle next to it on the same straight line? (a) 75° (b) 15° (c) 105° (d) 285°
  35. 35.Two angles of a triangle are 70° and 65°. What is the exterior angle at the third corner? (a) 110° (b) 135° (c) 115° (d) 45°
  36. 36.Two straight lines cross. One of the angles is 30°. What is the angle next to it on the same straight line? (a) 30° (b) 330° (c) 60° (d) 150°
  37. 37.Two angles of a triangle are 70° and 75°. What is the third angle? (a) 145° (b) 105° (c) 35° (d) 110°
  38. 38.Two straight lines cross. One of the angles is 100°. What is the angle next to it on the same straight line? (a) 80° (b) 81° (c) 100° (d) 260°
  39. 39.In an isosceles triangle, the angle between the two equal sides is 120°. What is each of the other two angles? (a) 40° (b) 120° (c) 60° (d) 30°
  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) 225° (c) 45° (d) 135°

Answer key

  1. 95°
  2. 130°
  3. 75°
  4. 155°
  5. 85°
  6. 45°
  7. 60°
  8. 70°
  9. 150°
  10. 15°
  11. 145°
  12. 50°
  13. 100°
  14. 60°
  15. 110°
  16. 160°
  17. 25°
  18. 100°
  19. 130°
  20. 65°
  21. 85°
  22. 70°
  23. 90°
  24. 140°
  25. 140°
  26. 65°
  27. 75°
  28. 85°
  29. 135°
  30. 50°
  31. 60°
  32. 10°
  33. 20°
  34. 105°
  35. 135°
  36. 150°
  37. 35°
  38. 80°
  39. 30°
  40. 45°

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