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Finding the Third Proportional to 78 and 90

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Solution

The third proportional to 78 and 90 is: 103.85

Step by Step Solution

  1. Step 1: Write the proportion equation
    78 : 90 = 90 : x
  2. Step 2: Convert to fraction form
    78/90 = 90/x
  3. Step 3: Cross multiply
    78x = 90 × 90
  4. Step 4: Simplify right side
    78x = 8,100
  5. Step 5: Solve for x
    x = 8,100/78
  6. Step 6: Final answer
    x = 103.85

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Why These Related Problems?

These problems maintain the same ratio (1.15) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.