silemus.
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  1. 4No solution, linear system
  2. 5Infinite solutions, linear system
  3. 15Probability from a table
  4. 18Median from a frequency table
  5. 22One solution, discriminant=0
  6. 23Max height of a parabola
  7. 25Exponential decay, 15% off
  8. 29Composing f and g
  9. 32Radius from two points
  10. 33Arc length from central angle
  11. 37Similar triangles ratio
  12. 47Two-ticket system of equations
  13. 51No solution, linear equation
  14. 52Taxi cost inequality
  15. 55Scaling 9x-6y+5
  16. 56Costly text message inequality
  17. 59Solving a square root equation
  18. 62Factor theorem on a cubic
  19. 64Percent growth per year
  20. 66x²+y² from sum and product
  21. 67Sum of roots of intersection
  22. 70Completing the square
  23. 73Percent off, then tax
  24. 74Mean with a score removed
  25. 75Overlapping sets, neither
  26. 81Percent of a percent
  27. 82Average speed, unequal times
  28. 85Fraction of a subgroup
  29. 86Mixing to a target percent
  30. 92Inscribed angle theorem
  31. 93Circle from diameter endpoints
  32. 96Sine-cosine complementary angles
  33. 97Area ratio of similar triangles
  34. 98Diagonal of a rectangle
  35. 100Right triangle, tan from cos
  36. 101Volume displaced raises water

37Similar triangles ratio

In triangle ABC, D is on AB and E is on AC so that DE is parallel to BC. AD = 6, DB = 4 and DE = 9. What is the length of BC? A) 12 B) 13.5 C) 15 D) 18

BC = 15, choice C. Since DE ∥ BC, triangle ADE ~ triangle ABC, so AD/AB = DE/BC. With AD=6, AB=10, DE=9, you get 6/10 = 9/BC, so BC = 90/6 = 15.

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