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Angles and Triangles Worksheet for Maths Olympiad

Maths Olympiad topic 21: Angles and triangles · Set 179 · 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) 55° (c) 325° (d) 145°
  2. 2.Two angles of a triangle are 20° and 100°. What is the exterior angle at the third corner? (a) 120° (b) 80° (c) 160° (d) 60°
  3. 3.Two straight lines cross. Two vertically opposite angles add up to 80°. What is each of the other two angles? (a) 100° (b) 140° (c) 40° (d) 280°
  4. 4.In an isosceles triangle, the angle between the two equal sides is 160°. What is each of the other two angles? (a) 160° (b) 20° (c) 11° (d) 10°
  5. 5.Two angles of a triangle are 55° and 90°. What is the exterior angle at the third corner? (a) 35° (b) 145° (c) 125° (d) 90°
  6. 6.Two angles of a triangle are 70° and 90°. What is the third angle? (a) 160° (b) 20° (c) 110° (d) 90°
  7. 7.Two angles of a triangle are 50° and 65°. What is the exterior angle at the third corner? (a) 130° (b) 65° (c) 245° (d) 115°
  8. 8.Two angles of a triangle are 50° and 85°. What is the exterior angle at the third corner? (a) 95° (b) 135° (c) 45° (d) 130°
  9. 9.Two straight lines cross. One of the angles is 95°. What is the angle next to it on the same straight line? (a) 265° (b) 85° (c) 95° (d) 86°
  10. 10.Two straight lines cross. One of the angles is 165°. What is the angle next to it on the same straight line? (a) 16° (b) 15° (c) 165° (d) 195°
  11. 11.Two angles of a triangle are 50° and 70°. What is the third angle? (a) 120° (b) 130° (c) 110° (d) 60°
  12. 12.In an isosceles triangle, the angle between the two equal sides is 80°. What is each of the other two angles? (a) 50° (b) 100° (c) 80° (d) 10°
  13. 13.In an isosceles triangle, the angle between the two equal sides is 20°. What is each of the other two angles? (a) 70° (b) 20° (c) 80° (d) 160°
  14. 14.Two angles of a triangle are 35° and 50°. What is the third angle? (a) 85° (b) 130° (c) 95° (d) 145°
  15. 15.Two angles of a triangle are 65° and 25°. What is the exterior angle at the third corner? (a) 155° (b) 115° (c) 90° (d) 270°
  16. 16.Two angles of a triangle are 75° and 55°. What is the third angle? (a) 50° (b) 125° (c) 105° (d) 130°
  17. 17.Two straight lines cross. One of the angles is 45°. What is the angle next to it on the same straight line? (a) 135° (b) 45° (c) 136° (d) 315°
  18. 18.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles? (a) 30° (b) 140° (c) 20° (d) 40°
  19. 19.Two angles of a triangle are 35° and 30°. What is the third angle? (a) 65° (b) 150° (c) 115° (d) 145°
  20. 20.Two straight lines cross. Two vertically opposite angles add up to 280°. What is each of the other two angles? (a) 40° (b) 41° (c) 140° (d) 80°
  21. 21.Two angles of a triangle are 20° and 55°. What is the exterior angle at the third corner? (a) 75° (b) 105° (c) 125° (d) 160°
  22. 22.In an isosceles triangle, the angle between the two equal sides is 70°. What is each of the other two angles? (a) 110° (b) 70° (c) 55° (d) 20°
  23. 23.Two angles of a triangle are 40° and 60°. What is the exterior angle at the third corner? (a) 140° (b) 120° (c) 100° (d) 80°
  24. 24.Two angles of a triangle are 65° and 50°. What is the third angle? (a) 115° (b) 65° (c) 130° (d) 245°
  25. 25.In an isosceles triangle, the two equal angles are 75° each. What is the third angle? (a) 75° (b) 30° (c) 105° (d) 15°
  26. 26.In an isosceles triangle, the two equal angles are 70° each. What is the third angle? (a) 70° (b) 110° (c) 20° (d) 40°
  27. 27.Two straight lines cross. Two vertically opposite angles add up to 150°. What is each of the other two angles? (a) 210° (b) 30° (c) 105° (d) 75°
  28. 28.Two angles of a triangle are 35° and 70°. What is the third angle? (a) 145° (b) 110° (c) 75° (d) 105°
  29. 29.Two straight lines cross. Two vertically opposite angles add up to 110°. What is each of the other two angles? (a) 55° (b) 125° (c) 250° (d) 70°
  30. 30.Two angles of a triangle are 40° and 30°. What is the exterior angle at the third corner? (a) 70° (b) 110° (c) 140° (d) 150°
  31. 31.Two angles of a triangle are 30° and 40°. What is the exterior angle at the third corner? (a) 140° (b) 150° (c) 70° (d) 110°
  32. 32.Two angles of a triangle are 20° and 105°. What is the third angle? (a) 125° (b) 55° (c) 160° (d) 75°
  33. 33.Two angles of a triangle are 25° and 65°. What is the third angle? (a) 115° (b) 90° (c) 155° (d) 270°
  34. 34.Two angles of a triangle are 75° and 90°. What is the third angle? (a) 15° (b) 90° (c) 105° (d) 165°
  35. 35.Two angles of a triangle are 30° and 90°. What is the third angle? (a) 90° (b) 60° (c) 150° (d) 120°
  36. 36.Two angles of a triangle are 25° and 20°. What is the exterior angle at the third corner? (a) 160° (b) 155° (c) 135° (d) 45°
  37. 37.Two angles of a triangle are 40° and 45°. What is the exterior angle at the third corner? (a) 95° (b) 135° (c) 85° (d) 140°
  38. 38.Two angles of a triangle are 60° and 30°. What is the third angle? (a) 270° (b) 150° (c) 90° (d) 120°
  39. 39.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°
  40. 40.Two straight lines cross. Two vertically opposite angles add up to 50°. What is each of the other two angles? (a) 155° (b) 25° (c) 130° (d) 310°

Answer key

  1. 145°
  2. 120°
  3. 140°
  4. 10°
  5. 145°
  6. 20°
  7. 115°
  8. 135°
  9. 85°
  10. 15°
  11. 60°
  12. 50°
  13. 80°
  14. 95°
  15. 90°
  16. 50°
  17. 135°
  18. 20°
  19. 115°
  20. 40°
  21. 75°
  22. 55°
  23. 100°
  24. 65°
  25. 30°
  26. 40°
  27. 105°
  28. 75°
  29. 125°
  30. 70°
  31. 70°
  32. 55°
  33. 90°
  34. 15°
  35. 60°
  36. 45°
  37. 85°
  38. 90°
  39. 35°
  40. 155°

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