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Finding the Fourth Proportional to 138.95, 208.45 and 81.18

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Solution

The fourth proportional to 138.95, 208.45 and 81.18 is: 121.78

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.95 : 208.45 = 81.18 : x
  2. Step 2: Convert to fraction form
    138.95/208.45 = 81.18/x
  3. Step 3: Cross multiply
    138.95x = 208.45 × 81.18
  4. Step 4: Simplify right side
    138.95x = 16,921.97
  5. Step 5: Solve for x
    x = 16,921.97/138.95
  6. Step 6: Final answer
    x = 121.78

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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.