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Finding the Fourth Proportional to 138.72, 208.14 and 128.40

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Solution

The fourth proportional to 138.72, 208.14 and 128.40 is: 192.66

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.72 : 208.14 = 128.40 : x
  2. Step 2: Convert to fraction form
    138.72/208.14 = 128.40/x
  3. Step 3: Cross multiply
    138.72x = 208.14 × 128.40
  4. Step 4: Simplify right side
    138.72x = 26,725.18
  5. Step 5: Solve for x
    x = 26,725.18/138.72
  6. Step 6: Final answer
    x = 192.66

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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.