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Finding the Fourth Proportional to 428.05, 642 and 139.48

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Solution

The fourth proportional to 428.05, 642 and 139.48 is: 209.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.05 : 642 = 139.48 : x
  2. Step 2: Convert to fraction form
    428.05/642 = 139.48/x
  3. Step 3: Cross multiply
    428.05x = 642 × 139.48
  4. Step 4: Simplify right side
    428.05x = 89,546.16
  5. Step 5: Solve for x
    x = 89,546.16/428.05
  6. Step 6: Final answer
    x = 209.20

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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.