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Finding the Fourth Proportional to 81.78, 121.96 and 78.74

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Solution

The fourth proportional to 81.78, 121.96 and 78.74 is: 117.43

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.78 : 121.96 = 78.74 : x
  2. Step 2: Convert to fraction form
    81.78/121.96 = 78.74/x
  3. Step 3: Cross multiply
    81.78x = 121.96 × 78.74
  4. Step 4: Simplify right side
    81.78x = 9,603.24
  5. Step 5: Solve for x
    x = 9,603.24/81.78
  6. Step 6: Final answer
    x = 117.43

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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.