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Finding the Fourth Proportional to 86.45, 128.87 and 81.89

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Solution

The fourth proportional to 86.45, 128.87 and 81.89 is: 122.07

Step by Step Solution

  1. Step 1: Write the proportion equation
    86.45 : 128.87 = 81.89 : x
  2. Step 2: Convert to fraction form
    86.45/128.87 = 81.89/x
  3. Step 3: Cross multiply
    86.45x = 128.87 × 81.89
  4. Step 4: Simplify right side
    86.45x = 10,552.11
  5. Step 5: Solve for x
    x = 10,552.11/86.45
  6. Step 6: Final answer
    x = 122.07

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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.