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Finding the Fourth Proportional to 20.81, 31.24 and 13.21

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Solution

The fourth proportional to 20.81, 31.24 and 13.21 is: 19.83

Step by Step Solution

  1. Step 1: Write the proportion equation
    20.81 : 31.24 = 13.21 : x
  2. Step 2: Convert to fraction form
    20.81/31.24 = 13.21/x
  3. Step 3: Cross multiply
    20.81x = 31.24 × 13.21
  4. Step 4: Simplify right side
    20.81x = 412.68
  5. Step 5: Solve for x
    x = 412.68/20.81
  6. Step 6: Final answer
    x = 19.83

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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.