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Finding the Fourth Proportional to 81.72, 121.80 and 78.12

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Solution

The fourth proportional to 81.72, 121.80 and 78.12 is: 116.43

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.72 : 121.80 = 78.12 : x
  2. Step 2: Convert to fraction form
    81.72/121.80 = 78.12/x
  3. Step 3: Cross multiply
    81.72x = 121.80 × 78.12
  4. Step 4: Simplify right side
    81.72x = 9,515.02
  5. Step 5: Solve for x
    x = 9,515.02/81.72
  6. Step 6: Final answer
    x = 116.43

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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.