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Finding the Fourth Proportional to 427.20, 640.78 and 138.64

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Solution

The fourth proportional to 427.20, 640.78 and 138.64 is: 207.95

Step by Step Solution

  1. Step 1: Write the proportion equation
    427.20 : 640.78 = 138.64 : x
  2. Step 2: Convert to fraction form
    427.20/640.78 = 138.64/x
  3. Step 3: Cross multiply
    427.20x = 640.78 × 138.64
  4. Step 4: Simplify right side
    427.20x = 88,837.74
  5. Step 5: Solve for x
    x = 88,837.74/427.20
  6. Step 6: Final answer
    x = 207.95

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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.