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Finding the Fourth Proportional to 85.45, 128.28 and 81.76

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Solution

The fourth proportional to 85.45, 128.28 and 81.76 is: 122.74

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.45 : 128.28 = 81.76 : x
  2. Step 2: Convert to fraction form
    85.45/128.28 = 81.76/x
  3. Step 3: Cross multiply
    85.45x = 128.28 × 81.76
  4. Step 4: Simplify right side
    85.45x = 10,488.17
  5. Step 5: Solve for x
    x = 10,488.17/85.45
  6. Step 6: Final answer
    x = 122.74

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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.