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Finding the Fourth Proportional to 85.91, 128.70 and 76.79

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Solution

The fourth proportional to 85.91, 128.70 and 76.79 is: 115.05

Step by Step Solution

  1. Step 1: Write the proportion equation
    85.91 : 128.70 = 76.79 : x
  2. Step 2: Convert to fraction form
    85.91/128.70 = 76.79/x
  3. Step 3: Cross multiply
    85.91x = 128.70 × 76.79
  4. Step 4: Simplify right side
    85.91x = 9,883.19
  5. Step 5: Solve for x
    x = 9,883.19/85.91
  6. Step 6: Final answer
    x = 115.05

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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.