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Finding the Fourth Proportional to 87.15, 129.78 and 81.91

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Solution

The fourth proportional to 87.15, 129.78 and 81.91 is: 121.98

Step by Step Solution

  1. Step 1: Write the proportion equation
    87.15 : 129.78 = 81.91 : x
  2. Step 2: Convert to fraction form
    87.15/129.78 = 81.91/x
  3. Step 3: Cross multiply
    87.15x = 129.78 × 81.91
  4. Step 4: Simplify right side
    87.15x = 10,630.28
  5. Step 5: Solve for x
    x = 10,630.28/87.15
  6. Step 6: Final answer
    x = 121.98

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Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.