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Finding the Fourth Proportional to 81.72, 122.57 and 20.85

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Solution

The fourth proportional to 81.72, 122.57 and 20.85 is: 31.27

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.72 : 122.57 = 20.85 : x
  2. Step 2: Convert to fraction form
    81.72/122.57 = 20.85/x
  3. Step 3: Cross multiply
    81.72x = 122.57 × 20.85
  4. Step 4: Simplify right side
    81.72x = 2,555.58
  5. Step 5: Solve for x
    x = 2,555.58/81.72
  6. Step 6: Final answer
    x = 31.27

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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.