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Finding the Fourth Proportional to 139.30, 208.78 and 81.61

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Solution

The fourth proportional to 139.30, 208.78 and 81.61 is: 122.32

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.30 : 208.78 = 81.61 : x
  2. Step 2: Convert to fraction form
    139.30/208.78 = 81.61/x
  3. Step 3: Cross multiply
    139.30x = 208.78 × 81.61
  4. Step 4: Simplify right side
    139.30x = 17,038.54
  5. Step 5: Solve for x
    x = 17,038.54/139.30
  6. Step 6: Final answer
    x = 122.32

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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.