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Angles and Triangles Worksheet for Maths Olympiad

Maths Olympiad topic 21: Angles and triangles · Set 148 · 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.In an isosceles triangle, the two equal angles are 35° each. What is the third angle? (a) 55° (b) 145° (c) 35° (d) 110°
  2. 2.In an isosceles triangle, the two equal angles are 85° each. What is the third angle? (a) 95° (b) 85° (c) 5° (d) 10°
  3. 3.Two angles of a triangle are 50° and 30°. What is the third angle? (a) 150° (b) 100° (c) 130° (d) 80°
  4. 4.Two angles of a triangle are 45° and 75°. What is the exterior angle at the third corner? (a) 105° (b) 135° (c) 60° (d) 120°
  5. 5.Two angles of a triangle are 35° and 80°. What is the third angle? (a) 100° (b) 145° (c) 65° (d) 115°
  6. 6.Two straight lines cross. One of the angles is 135°. What is the angle next to it on the same straight line? (a) 225° (b) 45° (c) 46° (d) 135°
  7. 7.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles? (a) 80° (b) 160° (c) 20° (d) 70°
  8. 8.Two angles of a triangle are 25° and 45°. What is the third angle? (a) 135° (b) 110° (c) 155° (d) 70°
  9. 9.Two angles of a triangle are 20° and 115°. What is the exterior angle at the third corner? (a) 135° (b) 45° (c) 65° (d) 160°
  10. 10.Two angles of a triangle are 55° and 90°. What is the exterior angle at the third corner? (a) 145° (b) 125° (c) 90° (d) 35°
  11. 11.Two angles of a triangle are 50° and 75°. What is the exterior angle at the third corner? (a) 55° (b) 105° (c) 130° (d) 125°
  12. 12.In an isosceles triangle, the two equal angles are 80° each. What is the third angle? (a) 10° (b) 20° (c) 80° (d) 100°
  13. 13.Two angles of a triangle are 25° and 125°. What is the third angle? (a) 55° (b) 150° (c) 30° (d) 155°
  14. 14.Two straight lines cross. Two vertically opposite angles add up to 40°. What is each of the other two angles? (a) 160° (b) 320° (c) 20° (d) 140°
  15. 15.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°
  16. 16.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) 320° (c) 140° (d) 40°
  17. 17.Two angles of a triangle are 75° and 95°. What is the third angle? (a) 170° (b) 105° (c) 85° (d) 10°
  18. 18.Two angles of a triangle are 60° and 60°. What is the third angle? (a) 240° (b) 61° (c) 60° (d) 120°
  19. 19.Two angles of a triangle are 65° and 90°. What is the third angle? (a) 115° (b) 90° (c) 155° (d) 25°
  20. 20.Two angles of a triangle are 45° and 85°. What is the third angle? (a) 130° (b) 135° (c) 95° (d) 50°
  21. 21.Two straight lines cross. Two vertically opposite angles add up to 340°. What is each of the other two angles? (a) 20° (b) 11° (c) 170° (d) 10°
  22. 22.In an isosceles triangle, the angle between the two equal sides is 110°. What is each of the other two angles? (a) 70° (b) 110° (c) 45° (d) 35°
  23. 23.Two angles of a triangle are 80° and 25°. What is the third angle? (a) 105° (b) 155° (c) 100° (d) 75°
  24. 24.In an isosceles triangle, the two equal angles are 25° each. What is the third angle? (a) 25° (b) 130° (c) 65° (d) 155°
  25. 25.Two angles of a triangle are 80° and 45°. What is the exterior angle at the third corner? (a) 100° (b) 125° (c) 55° (d) 135°
  26. 26.In an isosceles triangle, the angle between the two equal sides is 150°. What is each of the other two angles? (a) 25° (b) 15° (c) 150° (d) 30°
  27. 27.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles? (a) 110° (b) 20° (c) 70° (d) 55°
  28. 28.Two angles of a triangle are 30° and 100°. What is the exterior angle at the third corner? (a) 130° (b) 50° (c) 80° (d) 150°
  29. 29.Two angles of a triangle are 25° and 105°. What is the third angle? (a) 130° (b) 155° (c) 50° (d) 75°
  30. 30.Two angles of a triangle are 40° and 55°. What is the exterior angle at the third corner? (a) 125° (b) 140° (c) 85° (d) 95°
  31. 31.Two angles of a triangle are 25° and 70°. What is the third angle? (a) 155° (b) 110° (c) 85° (d) 95°
  32. 32.Two angles of a triangle are 50° and 90°. What is the exterior angle at the third corner? (a) 40° (b) 90° (c) 140° (d) 130°
  33. 33.Two angles of a triangle are 45° and 25°. What is the third angle? (a) 110° (b) 155° (c) 70° (d) 135°
  34. 34.Two angles of a triangle are 20° and 75°. What is the exterior angle at the third corner? (a) 85° (b) 160° (c) 95° (d) 105°
  35. 35.Two angles of a triangle are 75° and 40°. What is the third angle? (a) 65° (b) 115° (c) 140° (d) 105°
  36. 36.Two straight lines cross. One of the angles is 140°. What is the angle next to it on the same straight line? (a) 220° (b) 41° (c) 140° (d) 40°
  37. 37.In an isosceles triangle, the two equal angles are 55° each. What is the third angle? (a) 35° (b) 125° (c) 70° (d) 55°
  38. 38.Two angles of a triangle are 65° and 35°. What is the exterior angle at the third corner? (a) 145° (b) 80° (c) 115° (d) 100°
  39. 39.In an isosceles triangle, the two equal angles are 60° each. What is the third angle? (a) 61° (b) 60° (c) 120° (d) 30°
  40. 40.Two straight lines cross. One of the angles is 65°. What is the angle next to it on the same straight line? (a) 295° (b) 25° (c) 65° (d) 115°

Answer key

  1. 110°
  2. 10°
  3. 100°
  4. 120°
  5. 65°
  6. 45°
  7. 80°
  8. 110°
  9. 135°
  10. 145°
  11. 125°
  12. 20°
  13. 30°
  14. 160°
  15. 25°
  16. 140°
  17. 10°
  18. 60°
  19. 25°
  20. 50°
  21. 10°
  22. 35°
  23. 75°
  24. 130°
  25. 125°
  26. 15°
  27. 55°
  28. 130°
  29. 50°
  30. 95°
  31. 85°
  32. 140°
  33. 110°
  34. 95°
  35. 65°
  36. 40°
  37. 70°
  38. 100°
  39. 60°
  40. 115°

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