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Finding the Fourth Proportional to 39.78, 54.90 and 28.85

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Solution

The fourth proportional to 39.78, 54.90 and 28.85 is: 39.81

Step by Step Solution

  1. Step 1: Write the proportion equation
    39.78 : 54.90 = 28.85 : x
  2. Step 2: Convert to fraction form
    39.78/54.90 = 28.85/x
  3. Step 3: Cross multiply
    39.78x = 54.90 × 28.85
  4. Step 4: Simplify right side
    39.78x = 1,583.59
  5. Step 5: Solve for x
    x = 1,583.59/39.78
  6. Step 6: Final answer
    x = 39.81

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.