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Finding the Fourth Proportional to 138.75, 208.11 and 81

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Solution

The fourth proportional to 138.75, 208.11 and 81 is: 121.49

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.75 : 208.11 = 81 : x
  2. Step 2: Convert to fraction form
    138.75/208.11 = 81/x
  3. Step 3: Cross multiply
    138.75x = 208.11 × 81
  4. Step 4: Simplify right side
    138.75x = 16,856.64
  5. Step 5: Solve for x
    x = 16,856.64/138.75
  6. Step 6: Final answer
    x = 121.49

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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.