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Finding the Fourth Proportional to 20.78, 31.17 and 12.80

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Solution

The fourth proportional to 20.78, 31.17 and 12.80 is: 19.20

Step by Step Solution

  1. Step 1: Write the proportion equation
    20.78 : 31.17 = 12.80 : x
  2. Step 2: Convert to fraction form
    20.78/31.17 = 12.80/x
  3. Step 3: Cross multiply
    20.78x = 31.17 × 12.80
  4. Step 4: Simplify right side
    20.78x = 398.98
  5. Step 5: Solve for x
    x = 398.98/20.78
  6. Step 6: Final answer
    x = 19.20

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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.