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Angles and Triangles Worksheet for Maths Olympiad

Maths Olympiad topic 21: Angles and triangles · Set 88 · 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 20° and 90°. What is the exterior angle at the third corner? (a) 90° (b) 70° (c) 110° (d) 160°
  2. 2.In an isosceles triangle, the two equal angles are 35° each. What is the third angle? (a) 145° (b) 35° (c) 110° (d) 55°
  3. 3.Two angles of a triangle are 20° and 85°. What is the third angle? (a) 75° (b) 95° (c) 160° (d) 105°
  4. 4.Two angles of a triangle are 65° and 70°. What is the third angle? (a) 110° (b) 115° (c) 45° (d) 135°
  5. 5.Two angles of a triangle are 40° and 80°. What is the third angle? (a) 140° (b) 120° (c) 100° (d) 60°
  6. 6.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) 70° (c) 290° (d) 110°
  7. 7.Two straight lines cross. Two vertically opposite angles add up to 190°. What is each of the other two angles? (a) 85° (b) 95° (c) 86° (d) 170°
  8. 8.Two angles of a triangle are 30° and 35°. What is the exterior angle at the third corner? (a) 65° (b) 150° (c) 145° (d) 115°
  9. 9.Two angles of a triangle are 50° and 115°. What is the third angle? (a) 130° (b) 165° (c) 65° (d) 15°
  10. 10.Two straight lines cross. One of the angles is 20°. What is the angle next to it on the same straight line? (a) 160° (b) 20° (c) 340° (d) 70°
  11. 11.Two straight lines cross. One of the angles is 95°. What is the angle next to it on the same straight line? (a) 86° (b) 95° (c) 265° (d) 85°
  12. 12.In an isosceles triangle, the two equal angles are 85° each. What is the third angle? (a) 95° (b) 85° (c) 5° (d) 10°
  13. 13.In an isosceles triangle, the two equal angles are 75° each. What is the third angle? (a) 15° (b) 30° (c) 75° (d) 105°
  14. 14.Two angles of a triangle are 35° and 90°. What is the third angle? (a) 55° (b) 90° (c) 145° (d) 125°
  15. 15.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles? (a) 150° (b) 60° (c) 30° (d) 75°
  16. 16.Two angles of a triangle are 25° and 55°. What is the exterior angle at the third corner? (a) 100° (b) 125° (c) 80° (d) 155°
  17. 17.Two angles of a triangle are 65° and 85°. What is the exterior angle at the third corner? (a) 30° (b) 150° (c) 95° (d) 115°
  18. 18.Two straight lines cross. One of the angles is 40°. What is the angle next to it on the same straight line? (a) 50° (b) 140° (c) 40° (d) 320°
  19. 19.Two angles of a triangle are 75° and 25°. What is the exterior angle at the third corner? (a) 105° (b) 155° (c) 80° (d) 100°
  20. 20.Two angles of a triangle are 55° and 45°. What is the exterior angle at the third corner? (a) 125° (b) 135° (c) 80° (d) 100°
  21. 21.Two angles of a triangle are 25° and 35°. What is the third angle? (a) 145° (b) 120° (c) 60° (d) 155°
  22. 22.In an isosceles triangle, the angle between the two equal sides is 150°. What is each of the other two angles? (a) 25° (b) 150° (c) 15° (d) 30°
  23. 23.Two straight lines cross. One of the angles is 55°. What is the angle next to it on the same straight line? (a) 125° (b) 305° (c) 55° (d) 35°
  24. 24.Two angles of a triangle are 35° and 50°. What is the exterior angle at the third corner? (a) 145° (b) 95° (c) 130° (d) 85°
  25. 25.Two angles of a triangle are 50° and 75°. What is the exterior angle at the third corner? (a) 130° (b) 55° (c) 105° (d) 125°
  26. 26.In an isosceles triangle, the two equal angles are 55° each. What is the third angle? (a) 70° (b) 35° (c) 55° (d) 125°
  27. 27.Two angles of a triangle are 20° and 150°. What is the third angle? (a) 160° (b) 30° (c) 170° (d) 10°
  28. 28.Two angles of a triangle are 75° and 85°. What is the third angle? (a) 160° (b) 105° (c) 20° (d) 95°
  29. 29.Two angles of a triangle are 45° and 20°. What is the exterior angle at the third corner? (a) 135° (b) 115° (c) 65° (d) 160°
  30. 30.Two angles of a triangle are 70° and 25°. What is the third angle? (a) 95° (b) 85° (c) 110° (d) 155°
  31. 31.Two angles of a triangle are 60° and 60°. What is the third angle? (a) 61° (b) 60° (c) 120° (d) 240°
  32. 32.Two angles of a triangle are 80° and 40°. What is the exterior angle at the third corner? (a) 120° (b) 60° (c) 140° (d) 100°
  33. 33.Two angles of a triangle are 35° and 110°. What is the third angle? (a) 35° (b) 215° (c) 145° (d) 70°
  34. 34.Two angles of a triangle are 20° and 30°. What is the exterior angle at the third corner? (a) 160° (b) 130° (c) 50° (d) 150°
  35. 35.Two straight lines cross. One of the angles is 25°. What is the angle next to it on the same straight line? (a) 65° (b) 25° (c) 155° (d) 335°
  36. 36.Two angles of a triangle are 55° and 40°. What is the third angle? (a) 140° (b) 125° (c) 95° (d) 85°
  37. 37.Two straight lines cross. One of the angles is 155°. What is the angle next to it on the same straight line? (a) 155° (b) 25° (c) 205° (d) 26°
  38. 38.Two angles of a triangle are 45° and 100°. What is the third angle? (a) 145° (b) 135° (c) 35° (d) 80°
  39. 39.Two angles of a triangle are 40° and 125°. What is the third angle? (a) 55° (b) 140° (c) 15° (d) 165°
  40. 40.Two angles of a triangle are 25° and 90°. What is the exterior angle at the third corner? (a) 90° (b) 115° (c) 65° (d) 155°

Answer key

  1. 110°
  2. 110°
  3. 75°
  4. 45°
  5. 60°
  6. 110°
  7. 85°
  8. 65°
  9. 15°
  10. 160°
  11. 85°
  12. 10°
  13. 30°
  14. 55°
  15. 75°
  16. 80°
  17. 150°
  18. 140°
  19. 100°
  20. 100°
  21. 120°
  22. 15°
  23. 125°
  24. 85°
  25. 125°
  26. 70°
  27. 10°
  28. 20°
  29. 65°
  30. 85°
  31. 60°
  32. 120°
  33. 35°
  34. 50°
  35. 155°
  36. 85°
  37. 25°
  38. 35°
  39. 15°
  40. 115°

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