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Finding the Fourth Proportional to 138.78, 207.83 and 87.21

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Solution

The fourth proportional to 138.78, 207.83 and 87.21 is: 130.60

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.78 : 207.83 = 87.21 : x
  2. Step 2: Convert to fraction form
    138.78/207.83 = 87.21/x
  3. Step 3: Cross multiply
    138.78x = 207.83 × 87.21
  4. Step 4: Simplify right side
    138.78x = 18,125.07
  5. Step 5: Solve for x
    x = 18,125.07/138.78
  6. Step 6: Final answer
    x = 130.60

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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.