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Finding the Fourth Proportional to 138.70, 207.78 and 87.31

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Solution

The fourth proportional to 138.70, 207.78 and 87.31 is: 130.80

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.70 : 207.78 = 87.31 : x
  2. Step 2: Convert to fraction form
    138.70/207.78 = 87.31/x
  3. Step 3: Cross multiply
    138.70x = 207.78 × 87.31
  4. Step 4: Simplify right side
    138.70x = 18,141.27
  5. Step 5: Solve for x
    x = 18,141.27/138.70
  6. Step 6: Final answer
    x = 130.80

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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.