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Finding the Fourth Proportional to 428.31, 642.47 and 139.75

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Solution

The fourth proportional to 428.31, 642.47 and 139.75 is: 209.62

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.31 : 642.47 = 139.75 : x
  2. Step 2: Convert to fraction form
    428.31/642.47 = 139.75/x
  3. Step 3: Cross multiply
    428.31x = 642.47 × 139.75
  4. Step 4: Simplify right side
    428.31x = 89,781.97
  5. Step 5: Solve for x
    x = 89,781.97/428.31
  6. Step 6: Final answer
    x = 209.62

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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.