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Finding the Fourth Proportional to 139.89, 209.85 and 85.80

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Solution

The fourth proportional to 139.89, 209.85 and 85.80 is: 128.71

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.89 : 209.85 = 85.80 : x
  2. Step 2: Convert to fraction form
    139.89/209.85 = 85.80/x
  3. Step 3: Cross multiply
    139.89x = 209.85 × 85.80
  4. Step 4: Simplify right side
    139.89x = 18,005.13
  5. Step 5: Solve for x
    x = 18,005.13/139.89
  6. Step 6: Final answer
    x = 128.71

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.