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Finding the Fourth Proportional to 139.20, 208.80 and 85.44

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Solution

The fourth proportional to 139.20, 208.80 and 85.44 is: 128.16

Step by Step Solution

  1. Step 1: Write the proportion equation
    139.20 : 208.80 = 85.44 : x
  2. Step 2: Convert to fraction form
    139.20/208.80 = 85.44/x
  3. Step 3: Cross multiply
    139.20x = 208.80 × 85.44
  4. Step 4: Simplify right side
    139.20x = 17,839.87
  5. Step 5: Solve for x
    x = 17,839.87/139.20
  6. Step 6: Final answer
    x = 128.16

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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.