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Finding the Fourth Proportional to 81.78, 122.70 and 39

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Solution

The fourth proportional to 81.78, 122.70 and 39 is: 58.51

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.78 : 122.70 = 39 : x
  2. Step 2: Convert to fraction form
    81.78/122.70 = 39/x
  3. Step 3: Cross multiply
    81.78x = 122.70 × 39
  4. Step 4: Simplify right side
    81.78x = 4,785.30
  5. Step 5: Solve for x
    x = 4,785.30/81.78
  6. Step 6: Final answer
    x = 58.51

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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.