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Finding the Fourth Proportional to 138.12, 207.18 and 81

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Solution

The fourth proportional to 138.12, 207.18 and 81 is: 121.50

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.12 : 207.18 = 81 : x
  2. Step 2: Convert to fraction form
    138.12/207.18 = 81/x
  3. Step 3: Cross multiply
    138.12x = 207.18 × 81
  4. Step 4: Simplify right side
    138.12x = 16,781.58
  5. Step 5: Solve for x
    x = 16,781.58/138.12
  6. Step 6: Final answer
    x = 121.50

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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.