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Finding the Fourth Proportional to 428.36, 642.70 and 139.80

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Solution

The fourth proportional to 428.36, 642.70 and 139.80 is: 209.75

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.36 : 642.70 = 139.80 : x
  2. Step 2: Convert to fraction form
    428.36/642.70 = 139.80/x
  3. Step 3: Cross multiply
    428.36x = 642.70 × 139.80
  4. Step 4: Simplify right side
    428.36x = 89,849.46
  5. Step 5: Solve for x
    x = 89,849.46/428.36
  6. Step 6: Final answer
    x = 209.75

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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.