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Finding the Fourth Proportional to 428.35, 642.64 and 139.79

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Solution

The fourth proportional to 428.35, 642.64 and 139.79 is: 209.72

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.35 : 642.64 = 139.79 : x
  2. Step 2: Convert to fraction form
    428.35/642.64 = 139.79/x
  3. Step 3: Cross multiply
    428.35x = 642.64 × 139.79
  4. Step 4: Simplify right side
    428.35x = 89,831.08
  5. Step 5: Solve for x
    x = 89,831.08/428.35
  6. Step 6: Final answer
    x = 209.72

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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.