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Finding the Fourth Proportional to 139.20, 208.71 and 81.36

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Solution

The fourth proportional to 139.20, 208.71 and 81.36 is: 121.99

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.20 : 208.71 = 81.36 : x
  2. Step 2: Convert to fraction form
    139.20/208.71 = 81.36/x
  3. Step 3: Cross multiply
    139.20x = 208.71 × 81.36
  4. Step 4: Simplify right side
    139.20x = 16,980.65
  5. Step 5: Solve for x
    x = 16,980.65/139.20
  6. Step 6: Final answer
    x = 121.99

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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.