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Finding the Fourth Proportional to 85.78, 128.76 and 81.16

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Solution

The fourth proportional to 85.78, 128.76 and 81.16 is: 121.83

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.78 : 128.76 = 81.16 : x
  2. Step 2: Convert to fraction form
    85.78/128.76 = 81.16/x
  3. Step 3: Cross multiply
    85.78x = 128.76 × 81.16
  4. Step 4: Simplify right side
    85.78x = 10,450.16
  5. Step 5: Solve for x
    x = 10,450.16/85.78
  6. Step 6: Final answer
    x = 121.83

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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.