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Finding the Fourth Proportional to 85.61, 128.31 and 39.86

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Solution

The fourth proportional to 85.61, 128.31 and 39.86 is: 59.74

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.61 : 128.31 = 39.86 : x
  2. Step 2: Convert to fraction form
    85.61/128.31 = 39.86/x
  3. Step 3: Cross multiply
    85.61x = 128.31 × 39.86
  4. Step 4: Simplify right side
    85.61x = 5,114.44
  5. Step 5: Solve for x
    x = 5,114.44/85.61
  6. Step 6: Final answer
    x = 59.74

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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.