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Find a missing side of similar triangles

Year 8 maths · Fieldbook Learning

Name ______________________ Date __________

Find the scale factor from the matching sides, then use it on the side you need.

  1. Triangle ABC is similar to triangle DEF. AB = 5 cm, BC = 8 cm and DE = 10 cm. How long is EF, in cm?
  2. Triangle ABC is similar to triangle DEF. AB = 12 cm, BC = 10 cm and DE = 48 cm. How long is EF, in cm?
  3. Triangle ABC is similar to triangle DEF. AB = 11 cm, BC = 12 cm and DE = 33 cm. How long is EF, in cm?
  4. Triangle ABC is similar to triangle DEF. AB = 11 cm, BC = 8 cm and DE = 33 cm. How long is EF, in cm?
  5. Triangle ABC is similar to triangle DEF. AB = 12 cm, BC = 15 cm and DE = 24 cm. How long is EF, in cm?
  6. Triangle ABC is similar to triangle DEF. AB = 6 cm, BC = 11 cm and DE = 30 cm. How long is EF, in cm?
  7. Triangle ABC is similar to triangle DEF. AB = 4 cm, BC = 13 cm and DE = 12 cm. How long is EF, in cm?
  8. Triangle ABC is similar to triangle DEF. AB = 12 cm, BC = 11 cm and DE = 24 cm. How long is EF, in cm?
  9. Triangle ABC is similar to triangle DEF. AB = 17 cm, BC = 9 cm and DE = 85 cm. How long is EF, in cm?
  10. Triangle ABC is similar to triangle DEF. AB = 13 cm, BC = 8 cm and DE = 39 cm. How long is EF, in cm?
  11. Triangle ABC is similar to triangle DEF. AB = 17 cm, BC = 16 cm and DE = 85 cm. How long is EF, in cm?
  12. Triangle ABC is similar to triangle DEF. AB = 8 cm, BC = 14 cm and DE = 16 cm. How long is EF, in cm?
  13. Triangle ABC is similar to triangle DEF. AB = 10 cm, BC = 23 cm and DE = 80 cm. How long is EF, in cm?
  14. Triangle ABC is similar to triangle DEF. AB = 6 cm, BC = 7 cm and DE = 36 cm. How long is EF, in cm?
  15. Triangle ABC is similar to triangle DEF. AB = 23 cm, BC = 25 cm and DE = 184 cm. How long is EF, in cm?
  16. Triangle ABC is similar to triangle DEF. AB = 22 cm, BC = 11 cm and DE = 132 cm. How long is EF, in cm?
  17. Triangle ABC is similar to triangle DEF. AB = 17 cm, BC = 11 cm and DE = 153 cm. How long is EF, in cm?
  18. Triangle ABC is similar to triangle DEF. AB = 7 cm, BC = 11 cm and DE = 42 cm. How long is EF, in cm?
  19. Triangle ABC is similar to triangle DEF. AB = 14 cm, BC = 11 cm and DE = 70 cm. How long is EF, in cm?
  20. Triangle ABC is similar to triangle DEF. AB = 28 cm, BC = 15 cm and DE = 56 cm. How long is EF, in cm?
More free practice: fieldbooklearning.com/au/practice/year-8/find-a-missing-side-of-similar-triangles/

Play it as a quiz game

20 of these questions as multiple choice, with near-miss wrong answers, ready for Kahoot or Blooket.

  1. Download the game's own question template: in Kahoot, Add question → Import spreadsheet; in Blooket, Create a set → Spreadsheet import.
  2. Click the matching button below, then click the first empty question row of the template and paste.
  3. Save the template (Kahoot needs .xlsx, Blooket .csv) and upload it.
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Answer key: Find a missing side of similar triangles

  1. 16
  2. 40
  3. 36
  4. 24
  5. 30
  6. 55
  7. 39
  8. 22
  9. 45
  10. 24
  11. 80
  12. 28
  13. 184
  14. 42
  15. 200
  16. 66
  17. 99
  18. 66
  19. 55
  20. 30