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Finding the Fourth Proportional to 20.89, 31.28 and 12.31

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Solution

The fourth proportional to 20.89, 31.28 and 12.31 is: 18.42

Step by Step Solution

  1. Step 1: Write the proportion equation
    20.89 : 31.28 = 12.31 : x
  2. Step 2: Convert to fraction form
    20.89/31.28 = 12.31/x
  3. Step 3: Cross multiply
    20.89x = 31.28 × 12.31
  4. Step 4: Simplify right side
    20.89x = 384.92
  5. Step 5: Solve for x
    x = 384.92/20.89
  6. Step 6: Final answer
    x = 18.42

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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.