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Finding the Fourth Proportional to 428.72, 643.28 and 209.61

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Solution

The fourth proportional to 428.72, 643.28 and 209.61 is: 314.51

Step by Step Solution

  1. Step 1: Write the proportion equation
    428.72 : 643.28 = 209.61 : x
  2. Step 2: Convert to fraction form
    428.72/643.28 = 209.61/x
  3. Step 3: Cross multiply
    428.72x = 643.28 × 209.61
  4. Step 4: Simplify right side
    428.72x = 134,836.87
  5. Step 5: Solve for x
    x = 134,836.87/428.72
  6. Step 6: Final answer
    x = 314.51

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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.