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Finding the Fourth Proportional to 81.20, 121.90 and 80.70

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Solution

The fourth proportional to 81.20, 121.90 and 80.70 is: 121.15

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.20 : 121.90 = 80.70 : x
  2. Step 2: Convert to fraction form
    81.20/121.90 = 80.70/x
  3. Step 3: Cross multiply
    81.20x = 121.90 × 80.70
  4. Step 4: Simplify right side
    81.20x = 9,837.33
  5. Step 5: Solve for x
    x = 9,837.33/81.20
  6. Step 6: Final answer
    x = 121.15

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Why These Related Problems?

These problems maintain the same ratio (1.50) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.