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Finding the Fourth Proportional to 138.91, 208.20 and 81.16

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Solution

The fourth proportional to 138.91, 208.20 and 81.16 is: 121.64

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.91 : 208.20 = 81.16 : x
  2. Step 2: Convert to fraction form
    138.91/208.20 = 81.16/x
  3. Step 3: Cross multiply
    138.91x = 208.20 × 81.16
  4. Step 4: Simplify right side
    138.91x = 16,897.51
  5. Step 5: Solve for x
    x = 16,897.51/138.91
  6. Step 6: Final answer
    x = 121.64

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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.