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Finding the Fourth Proportional to 91.20, 125.85 and 78.90

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Solution

The fourth proportional to 91.20, 125.85 and 78.90 is: 108.88

Step by Step Solution

  1. Step 1: Write the proportion equation
    91.20 : 125.85 = 78.90 : x
  2. Step 2: Convert to fraction form
    91.20/125.85 = 78.90/x
  3. Step 3: Cross multiply
    91.20x = 125.85 × 78.90
  4. Step 4: Simplify right side
    91.20x = 9,929.57
  5. Step 5: Solve for x
    x = 9,929.57/91.20
  6. Step 6: Final answer
    x = 108.88

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.