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Finding the Fourth Proportional to 91.20, 136.80 and 86

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Solution

The fourth proportional to 91.20, 136.80 and 86 is: 129

Step by Step Solution

  1. Step 1: Write the proportion equation
    91.20 : 136.80 = 86 : x
  2. Step 2: Convert to fraction form
    91.20/136.80 = 86/x
  3. Step 3: Cross multiply
    91.20x = 136.80 × 86
  4. Step 4: Simplify right side
    91.20x = 11,764.80
  5. Step 5: Solve for x
    x = 11,764.80/91.20
  6. Step 6: Final answer
    x = 129

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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.