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Finding the Fourth Proportional to 138.75, 208.19 and 81.75

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Solution

The fourth proportional to 138.75, 208.19 and 81.75 is: 122.66

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.75 : 208.19 = 81.75 : x
  2. Step 2: Convert to fraction form
    138.75/208.19 = 81.75/x
  3. Step 3: Cross multiply
    138.75x = 208.19 × 81.75
  4. Step 4: Simplify right side
    138.75x = 17,019.53
  5. Step 5: Solve for x
    x = 17,019.53/138.75
  6. Step 6: Final answer
    x = 122.66

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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.