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Finding the Fourth Proportional to 81.76, 121.79 and 78.79

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Solution

The fourth proportional to 81.76, 121.79 and 78.79 is: 117.37

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.76 : 121.79 = 78.79 : x
  2. Step 2: Convert to fraction form
    81.76/121.79 = 78.79/x
  3. Step 3: Cross multiply
    81.76x = 121.79 × 78.79
  4. Step 4: Simplify right side
    81.76x = 9,595.83
  5. Step 5: Solve for x
    x = 9,595.83/81.76
  6. Step 6: Final answer
    x = 117.37

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Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.