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Finding the Fourth Proportional to 128.70, 192.78 and 80.64

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Solution

The fourth proportional to 128.70, 192.78 and 80.64 is: 120.79

Step by Step Solution

  1. Step 1: Write the proportion equation
    128.70 : 192.78 = 80.64 : x
  2. Step 2: Convert to fraction form
    128.70/192.78 = 80.64/x
  3. Step 3: Cross multiply
    128.70x = 192.78 × 80.64
  4. Step 4: Simplify right side
    128.70x = 15,545.78
  5. Step 5: Solve for x
    x = 15,545.78/128.70
  6. Step 6: Final answer
    x = 120.79

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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.