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Finding the Fourth Proportional to 81.78, 122.70 and 69.90

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Solution

The fourth proportional to 81.78, 122.70 and 69.90 is: 104.88

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.78 : 122.70 = 69.90 : x
  2. Step 2: Convert to fraction form
    81.78/122.70 = 69.90/x
  3. Step 3: Cross multiply
    81.78x = 122.70 × 69.90
  4. Step 4: Simplify right side
    81.78x = 8,576.73
  5. Step 5: Solve for x
    x = 8,576.73/81.78
  6. Step 6: Final answer
    x = 104.88

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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.