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Finding the Fourth Proportional to 428.20, 642.20 and 139.56

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Solution

The fourth proportional to 428.20, 642.20 and 139.56 is: 209.31

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.20 : 642.20 = 139.56 : x
  2. Step 2: Convert to fraction form
    428.20/642.20 = 139.56/x
  3. Step 3: Cross multiply
    428.20x = 642.20 × 139.56
  4. Step 4: Simplify right side
    428.20x = 89,625.43
  5. Step 5: Solve for x
    x = 89,625.43/428.20
  6. Step 6: Final answer
    x = 209.31

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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.