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Finding the Fourth Proportional to 21.20, 31.86 and 20.40

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Solution

The fourth proportional to 21.20, 31.86 and 20.40 is: 30.66

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.20 : 31.86 = 20.40 : x
  2. Step 2: Convert to fraction form
    21.20/31.86 = 20.40/x
  3. Step 3: Cross multiply
    21.20x = 31.86 × 20.40
  4. Step 4: Simplify right side
    21.20x = 649.94
  5. Step 5: Solve for x
    x = 649.94/21.20
  6. Step 6: Final answer
    x = 30.66

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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.