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Finding the Fourth Proportional to 81.20, 112.10 and 78.64

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Solution

The fourth proportional to 81.20, 112.10 and 78.64 is: 108.55

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.20 : 112.10 = 78.64 : x
  2. Step 2: Convert to fraction form
    81.20/112.10 = 78.64/x
  3. Step 3: Cross multiply
    81.20x = 112.10 × 78.64
  4. Step 4: Simplify right side
    81.20x = 8,814.87
  5. Step 5: Solve for x
    x = 8,814.87/81.20
  6. Step 6: Final answer
    x = 108.55

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.