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Finding the Fourth Proportional to 85.92, 128.78 and 51.21

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Solution

The fourth proportional to 85.92, 128.78 and 51.21 is: 76.75

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.92 : 128.78 = 51.21 : x
  2. Step 2: Convert to fraction form
    85.92/128.78 = 51.21/x
  3. Step 3: Cross multiply
    85.92x = 128.78 × 51.21
  4. Step 4: Simplify right side
    85.92x = 6,594.57
  5. Step 5: Solve for x
    x = 6,594.57/85.92
  6. Step 6: Final answer
    x = 76.75

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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.