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Finding the Fourth Proportional to 139.70, 209.45 and 81.91

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Solution

The fourth proportional to 139.70, 209.45 and 81.91 is: 122.81

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.70 : 209.45 = 81.91 : x
  2. Step 2: Convert to fraction form
    139.70/209.45 = 81.91/x
  3. Step 3: Cross multiply
    139.70x = 209.45 × 81.91
  4. Step 4: Simplify right side
    139.70x = 17,156.17
  5. Step 5: Solve for x
    x = 17,156.17/139.70
  6. Step 6: Final answer
    x = 122.81

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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.