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Angles and Triangles Worksheet for Maths Olympiad

Maths Olympiad topic 21: Angles and triangles · Set 549 · 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 50° and 85°. What is the third angle? (a) 135° (b) 130° (c) 95° (d) 45°
  2. 2.Two straight lines cross. One of the angles is 115°. What is the angle next to it on the same straight line? (a) 66° (b) 245° (c) 65° (d) 115°
  3. 3.Two angles of a triangle are 80° and 55°. What is the exterior angle at the third corner? (a) 100° (b) 125° (c) 135° (d) 45°
  4. 4.Two straight lines cross. Two vertically opposite angles add up to 280°. What is each of the other two angles? (a) 80° (b) 140° (c) 41° (d) 40°
  5. 5.Two angles of a triangle are 65° and 30°. What is the exterior angle at the third corner? (a) 150° (b) 85° (c) 95° (d) 115°
  6. 6.Two angles of a triangle are 70° and 35°. What is the third angle? (a) 75° (b) 110° (c) 105° (d) 145°
  7. 7.Two angles of a triangle are 20° and 75°. What is the third angle? (a) 105° (b) 85° (c) 95° (d) 160°
  8. 8.Two straight lines cross. Two vertically opposite angles add up to 70°. What is each of the other two angles? (a) 35° (b) 290° (c) 110° (d) 145°
  9. 9.Two angles of a triangle are 80° and 90°. What is the third angle? (a) 170° (b) 100° (c) 90° (d) 10°
  10. 10.Two straight lines cross. One of the angles is 130°. What is the angle next to it on the same straight line? (a) 130° (b) 50° (c) 51° (d) 230°
  11. 11.Two straight lines cross. Two vertically opposite angles add up to 320°. What is each of the other two angles? (a) 20° (b) 160° (c) 21° (d) 40°
  12. 12.Two angles of a triangle are 80° and 30°. What is the third angle? (a) 150° (b) 100° (c) 70° (d) 110°
  13. 13.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles? (a) 10° (b) 80° (c) 100° (d) 50°
  14. 14.Two angles of a triangle are 45° and 65°. What is the third angle? (a) 110° (b) 115° (c) 135° (d) 70°
  15. 15.Two straight lines cross. One of the angles is 120°. What is the angle next to it on the same straight line? (a) 61° (b) 120° (c) 240° (d) 60°
  16. 16.In an isosceles triangle, the angle between the two equal sides is 160°. What is each of the other two angles? (a) 11° (b) 20° (c) 10° (d) 160°
  17. 17.Two angles of a triangle are 40° and 35°. What is the third angle? (a) 140° (b) 145° (c) 75° (d) 105°
  18. 18.Two angles of a triangle are 60° and 35°. What is the third angle? (a) 95° (b) 85° (c) 120° (d) 145°
  19. 19.Two angles of a triangle are 25° and 105°. What is the third angle? (a) 155° (b) 50° (c) 130° (d) 75°
  20. 20.Two angles of a triangle are 55° and 80°. What is the exterior angle at the third corner? (a) 125° (b) 45° (c) 135° (d) 100°
  21. 21.Two straight lines cross. Two vertically opposite angles add up to 220°. What is each of the other two angles? (a) 71° (b) 140° (c) 110° (d) 70°
  22. 22.Two angles of a triangle are 70° and 90°. What is the third angle? (a) 110° (b) 160° (c) 90° (d) 20°
  23. 23.Two angles of a triangle are 60° and 55°. What is the exterior angle at the third corner? (a) 65° (b) 120° (c) 115° (d) 125°
  24. 24.Two straight lines cross. Two vertically opposite angles add up to 60°. What is each of the other two angles? (a) 300° (b) 30° (c) 150° (d) 120°
  25. 25.In an isosceles triangle, the angle between the two equal sides is 100°. What is each of the other two angles? (a) 80° (b) 50° (c) 100° (d) 40°
  26. 26.Two angles of a triangle are 65° and 75°. What is the exterior angle at the third corner? (a) 40° (b) 140° (c) 115° (d) 105°
  27. 27.Two angles of a triangle are 30° and 130°. What is the third angle? (a) 50° (b) 20° (c) 150° (d) 160°
  28. 28.Two angles of a triangle are 55° and 40°. What is the third angle? (a) 85° (b) 140° (c) 125° (d) 95°
  29. 29.In an isosceles triangle, the angle between the two equal sides is 150°. What is each of the other two angles? (a) 150° (b) 30° (c) 15° (d) 25°
  30. 30.Two angles of a triangle are 75° and 45°. What is the third angle? (a) 105° (b) 60° (c) 135° (d) 120°
  31. 31.Two straight lines cross. Two vertically opposite angles add up to 40°. What is each of the other two angles? (a) 20° (b) 320° (c) 140° (d) 160°
  32. 32.Two angles of a triangle are 30° and 100°. What is the exterior angle at the third corner? (a) 50° (b) 130° (c) 80° (d) 150°
  33. 33.Two angles of a triangle are 70° and 65°. What is the third angle? (a) 45° (b) 110° (c) 135° (d) 115°
  34. 34.Two angles of a triangle are 60° and 70°. What is the exterior angle at the third corner? (a) 50° (b) 120° (c) 110° (d) 130°
  35. 35.Two angles of a triangle are 50° and 65°. What is the third angle? (a) 130° (b) 245° (c) 115° (d) 65°
  36. 36.Two angles of a triangle are 25° and 25°. What is the third angle? (a) 130° (b) 310° (c) 155° (d) 50°
  37. 37.Two straight lines cross. One of the angles is 70°. What is the angle next to it on the same straight line? (a) 20° (b) 110° (c) 70° (d) 290°
  38. 38.Two angles of a triangle are 55° and 60°. What is the exterior angle at the third corner? (a) 125° (b) 65° (c) 120° (d) 115°
  39. 39.In an isosceles triangle, the two equal angles are 85° each. What is the third angle? (a) 85° (b) 5° (c) 10° (d) 95°
  40. 40.Two angles of a triangle are 40° and 85°. What is the third angle? (a) 125° (b) 95° (c) 140° (d) 55°

Answer key

  1. 45°
  2. 65°
  3. 135°
  4. 40°
  5. 95°
  6. 75°
  7. 85°
  8. 145°
  9. 10°
  10. 50°
  11. 20°
  12. 70°
  13. 50°
  14. 70°
  15. 60°
  16. 10°
  17. 105°
  18. 85°
  19. 50°
  20. 135°
  21. 70°
  22. 20°
  23. 115°
  24. 150°
  25. 40°
  26. 140°
  27. 20°
  28. 85°
  29. 15°
  30. 60°
  31. 160°
  32. 130°
  33. 45°
  34. 130°
  35. 65°
  36. 130°
  37. 110°
  38. 115°
  39. 10°
  40. 55°

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