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Finding the Fourth Proportional to 21.06, 31.39 and 20.61

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Solution

The fourth proportional to 21.06, 31.39 and 20.61 is: 30.72

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.06 : 31.39 = 20.61 : x
  2. Step 2: Convert to fraction form
    21.06/31.39 = 20.61/x
  3. Step 3: Cross multiply
    21.06x = 31.39 × 20.61
  4. Step 4: Simplify right side
    21.06x = 646.90
  5. Step 5: Solve for x
    x = 646.90/21.06
  6. Step 6: Final answer
    x = 30.72

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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.