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Finding the Fourth Proportional to 139.68, 209.59 and 81.90

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Solution

The fourth proportional to 139.68, 209.59 and 81.90 is: 122.89

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.68 : 209.59 = 81.90 : x
  2. Step 2: Convert to fraction form
    139.68/209.59 = 81.90/x
  3. Step 3: Cross multiply
    139.68x = 209.59 × 81.90
  4. Step 4: Simplify right side
    139.68x = 17,165.22
  5. Step 5: Solve for x
    x = 17,165.22/139.68
  6. Step 6: Final answer
    x = 122.89

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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.