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Finding the Fourth Proportional to 87.21, 129.94 and 81

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Solution

The fourth proportional to 87.21, 129.94 and 81 is: 120.68

Step by Step Solution

  1. Step 1: Write the proportion equation
    87.21 : 129.94 = 81 : x
  2. Step 2: Convert to fraction form
    87.21/129.94 = 81/x
  3. Step 3: Cross multiply
    87.21x = 129.94 × 81
  4. Step 4: Simplify right side
    87.21x = 10,524.94
  5. Step 5: Solve for x
    x = 10,524.94/87.21
  6. Step 6: Final answer
    x = 120.68

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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.