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Finding the Fourth Proportional to 138.87, 208.40 and 78.12

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Solution

The fourth proportional to 138.87, 208.40 and 78.12 is: 117.23

Step by Step Solution

  1. Step 1: Write the proportion equation
    138.87 : 208.40 = 78.12 : x
  2. Step 2: Convert to fraction form
    138.87/208.40 = 78.12/x
  3. Step 3: Cross multiply
    138.87x = 208.40 × 78.12
  4. Step 4: Simplify right side
    138.87x = 16,279.82
  5. Step 5: Solve for x
    x = 16,279.82/138.87
  6. Step 6: Final answer
    x = 117.23

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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.