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Angles and Triangles Worksheet for Maths Olympiad

Maths Olympiad topic 21: Angles and triangles · Set 983 · 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 45° and 20°. What is the third angle? (a) 160° (b) 135° (c) 65° (d) 115°
  2. 2.Two angles of a triangle are 70° and 90°. What is the third angle? (a) 160° (b) 110° (c) 20° (d) 90°
  3. 3.Two angles of a triangle are 65° and 25°. What is the third angle? (a) 115° (b) 155° (c) 90° (d) 270°
  4. 4.In an isosceles triangle, the angle between the two equal sides is 140°. What is each of the other two angles? (a) 30° (b) 20° (c) 140° (d) 40°
  5. 5.Two straight lines cross. One of the angles is 35°. What is the angle next to it on the same straight line? (a) 55° (b) 325° (c) 145° (d) 35°
  6. 6.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) 50° (c) 140° (d) 320°
  7. 7.Two angles of a triangle are 50° and 20°. What is the exterior angle at the third corner? (a) 110° (b) 160° (c) 70° (d) 130°
  8. 8.In an isosceles triangle, the two equal angles are 50° each. What is the third angle? (a) 40° (b) 50° (c) 80° (d) 130°
  9. 9.Two straight lines cross. One of the angles is 130°. What is the angle next to it on the same straight line? (a) 230° (b) 130° (c) 50° (d) 51°
  10. 10.Two straight lines cross. Two vertically opposite angles add up to 220°. What is each of the other two angles? (a) 70° (b) 110° (c) 71° (d) 140°
  11. 11.Two angles of a triangle are 30° and 25°. What is the exterior angle at the third corner? (a) 55° (b) 125° (c) 150° (d) 155°
  12. 12.Two angles of a triangle are 30° and 50°. What is the third angle? (a) 150° (b) 130° (c) 100° (d) 80°
  13. 13.In an isosceles triangle, the angle between the two equal sides is 90°. What is each of the other two angles? (a) 90° (b) 46° (c) 55° (d) 45°
  14. 14.Two angles of a triangle are 55° and 80°. What is the third angle? (a) 45° (b) 125° (c) 135° (d) 100°
  15. 15.In an isosceles triangle, the angle between the two equal sides is 30°. What is each of the other two angles? (a) 30° (b) 60° (c) 150° (d) 75°
  16. 16.Two straight lines cross. Two vertically opposite angles add up to 240°. What is each of the other two angles? (a) 59° (b) 60° (c) 61° (d) 120°
  17. 17.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) 20° (d) 55°
  18. 18.Two angles of a triangle are 25° and 120°. What is the exterior angle at the third corner? (a) 155° (b) 35° (c) 145° (d) 60°
  19. 19.In an isosceles triangle, the angle between the two equal sides is 60°. What is each of the other two angles? (a) 70° (b) 60° (c) 30° (d) 120°
  20. 20.Two angles of a triangle are 55° and 70°. What is the third angle? (a) 55° (b) 235° (c) 125° (d) 110°
  21. 21.Two straight lines cross. Two vertically opposite angles add up to 340°. What is each of the other two angles? (a) 170° (b) 11° (c) 10° (d) 20°
  22. 22.Two angles of a triangle are 65° and 20°. What is the exterior angle at the third corner? (a) 160° (b) 85° (c) 95° (d) 115°
  23. 23.Two angles of a triangle are 35° and 100°. What is the exterior angle at the third corner? (a) 135° (b) 80° (c) 145° (d) 45°
  24. 24.Two angles of a triangle are 45° and 20°. What is the exterior angle at the third corner? (a) 160° (b) 115° (c) 135° (d) 65°
  25. 25.Two angles of a triangle are 35° and 50°. What is the third angle? (a) 95° (b) 130° (c) 145° (d) 85°
  26. 26.Two angles of a triangle are 80° and 20°. What is the exterior angle at the third corner? (a) 100° (b) 160° (c) 260° (d) 80°
  27. 27.Two angles of a triangle are 35° and 95°. What is the exterior angle at the third corner? (a) 145° (b) 85° (c) 130° (d) 50°
  28. 28.Two angles of a triangle are 40° and 80°. What is the exterior angle at the third corner? (a) 100° (b) 60° (c) 140° (d) 120°
  29. 29.In an isosceles triangle, the two equal angles are 75° each. What is the third angle? (a) 75° (b) 105° (c) 30° (d) 15°
  30. 30.Two straight lines cross. One of the angles is 165°. What is the angle next to it on the same straight line? (a) 15° (b) 165° (c) 195° (d) 16°
  31. 31.Two straight lines cross. One of the angles is 110°. What is the angle next to it on the same straight line? (a) 250° (b) 70° (c) 110° (d) 71°
  32. 32.Two angles of a triangle are 30° and 45°. What is the third angle? (a) 105° (b) 75° (c) 150° (d) 135°
  33. 33.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°
  34. 34.Two angles of a triangle are 75° and 75°. What is the exterior angle at the third corner? (a) 30° (b) 210° (c) 150° (d) 105°
  35. 35.Two angles of a triangle are 45° and 60°. What is the exterior angle at the third corner? (a) 120° (b) 135° (c) 75° (d) 105°
  36. 36.Two angles of a triangle are 70° and 20°. What is the third angle? (a) 270° (b) 90° (c) 110° (d) 160°
  37. 37.Two angles of a triangle are 55° and 25°. What is the third angle? (a) 125° (b) 155° (c) 80° (d) 100°
  38. 38.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) 155° (c) 335° (d) 25°
  39. 39.Two angles of a triangle are 45° and 90°. What is the third angle? (a) 90° (b) 135° (c) 225° (d) 45°
  40. 40.In an isosceles triangle, the two equal angles are 65° each. What is the third angle? (a) 50° (b) 115° (c) 25° (d) 65°

Answer key

  1. 115°
  2. 20°
  3. 90°
  4. 20°
  5. 145°
  6. 140°
  7. 70°
  8. 80°
  9. 50°
  10. 70°
  11. 55°
  12. 100°
  13. 45°
  14. 45°
  15. 75°
  16. 60°
  17. 55°
  18. 145°
  19. 60°
  20. 55°
  21. 10°
  22. 85°
  23. 135°
  24. 65°
  25. 95°
  26. 100°
  27. 130°
  28. 120°
  29. 30°
  30. 15°
  31. 70°
  32. 105°
  33. 155°
  34. 150°
  35. 105°
  36. 90°
  37. 100°
  38. 155°
  39. 45°
  40. 50°

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