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Finding the Fourth Proportional to 428.25, 642.38 and 139.70

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Solution

The fourth proportional to 428.25, 642.38 and 139.70 is: 209.54

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.25 : 642.38 = 139.70 : x
  2. Step 2: Convert to fraction form
    428.25/642.38 = 139.70/x
  3. Step 3: Cross multiply
    428.25x = 642.38 × 139.70
  4. Step 4: Simplify right side
    428.25x = 89,736.58
  5. Step 5: Solve for x
    x = 89,736.58/428.25
  6. Step 6: Final answer
    x = 209.54

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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.