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Finding the Fourth Proportional to 139, 208.64 and 78.20

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Solution

The fourth proportional to 139, 208.64 and 78.20 is: 117.38

Step by Step Solution

  1. Step 1: Write the proportion equation
    139 : 208.64 = 78.20 : x
  2. Step 2: Convert to fraction form
    139/208.64 = 78.20/x
  3. Step 3: Cross multiply
    139x = 208.64 × 78.20
  4. Step 4: Simplify right side
    139x = 16,315.65
  5. Step 5: Solve for x
    x = 16,315.65/139
  6. Step 6: Final answer
    x = 117.38

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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.