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Finding the Fourth Proportional to 81.40, 122.84 and 78.72

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Solution

The fourth proportional to 81.40, 122.84 and 78.72 is: 118.80

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.40 : 122.84 = 78.72 : x
  2. Step 2: Convert to fraction form
    81.40/122.84 = 78.72/x
  3. Step 3: Cross multiply
    81.40x = 122.84 × 78.72
  4. Step 4: Simplify right side
    81.40x = 9,669.96
  5. Step 5: Solve for x
    x = 9,669.96/81.40
  6. Step 6: Final answer
    x = 118.80

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Why These Related Problems?

These problems maintain the same ratio (1.51) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.