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Finding the Fourth Proportional to 138.58, 207.87 and 81.20

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Solution

The fourth proportional to 138.58, 207.87 and 81.20 is: 121.80

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.58 : 207.87 = 81.20 : x
  2. Step 2: Convert to fraction form
    138.58/207.87 = 81.20/x
  3. Step 3: Cross multiply
    138.58x = 207.87 × 81.20
  4. Step 4: Simplify right side
    138.58x = 16,879.56
  5. Step 5: Solve for x
    x = 16,879.56/138.58
  6. Step 6: Final answer
    x = 121.80

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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.