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Finding the Fourth Proportional to 61.91, 85.39 and 39.78

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Solution

The fourth proportional to 61.91, 85.39 and 39.78 is: 54.87

Step by Step Solution

  1. Step 1: Write the proportion equation
    61.91 : 85.39 = 39.78 : x
  2. Step 2: Convert to fraction form
    61.91/85.39 = 39.78/x
  3. Step 3: Cross multiply
    61.91x = 85.39 × 39.78
  4. Step 4: Simplify right side
    61.91x = 3,396.95
  5. Step 5: Solve for x
    x = 3,396.95/61.91
  6. Step 6: Final answer
    x = 54.87

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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.