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Finding the Fourth Proportional to 91, 136.19 and 85.74

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Solution

The fourth proportional to 91, 136.19 and 85.74 is: 128.31

Step by Step Solution

  1. Step 1: Write the proportion equation
    91 : 136.19 = 85.74 : x
  2. Step 2: Convert to fraction form
    91/136.19 = 85.74/x
  3. Step 3: Cross multiply
    91x = 136.19 × 85.74
  4. Step 4: Simplify right side
    91x = 11,675.82
  5. Step 5: Solve for x
    x = 11,675.82/91
  6. Step 6: Final answer
    x = 128.31

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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.