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Finding the Fourth Proportional to 259.78, 389.69 and 86.40

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Solution

The fourth proportional to 259.78, 389.69 and 86.40 is: 129.61

Step by Step Solution

  1. Step 1: Write the proportion equation
    259.78 : 389.69 = 86.40 : x
  2. Step 2: Convert to fraction form
    259.78/389.69 = 86.40/x
  3. Step 3: Cross multiply
    259.78x = 389.69 × 86.40
  4. Step 4: Simplify right side
    259.78x = 33,669.22
  5. Step 5: Solve for x
    x = 33,669.22/259.78
  6. Step 6: Final answer
    x = 129.61

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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.