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Finding the Fourth Proportional to 138.78, 208.14 and 81.78

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Solution

The fourth proportional to 138.78, 208.14 and 81.78 is: 122.65

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.78 : 208.14 = 81.78 : x
  2. Step 2: Convert to fraction form
    138.78/208.14 = 81.78/x
  3. Step 3: Cross multiply
    138.78x = 208.14 × 81.78
  4. Step 4: Simplify right side
    138.78x = 17,021.69
  5. Step 5: Solve for x
    x = 17,021.69/138.78
  6. Step 6: Final answer
    x = 122.65

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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.