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Finding the Fourth Proportional to 85.72, 128.75 and 81.13

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Solution

The fourth proportional to 85.72, 128.75 and 81.13 is: 121.86

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.72 : 128.75 = 81.13 : x
  2. Step 2: Convert to fraction form
    85.72/128.75 = 81.13/x
  3. Step 3: Cross multiply
    85.72x = 128.75 × 81.13
  4. Step 4: Simplify right side
    85.72x = 10,445.49
  5. Step 5: Solve for x
    x = 10,445.49/85.72
  6. Step 6: Final answer
    x = 121.86

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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.