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Finding the Fourth Proportional to 21.28, 31.85 and 13.64

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Solution

The fourth proportional to 21.28, 31.85 and 13.64 is: 20.42

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.28 : 31.85 = 13.64 : x
  2. Step 2: Convert to fraction form
    21.28/31.85 = 13.64/x
  3. Step 3: Cross multiply
    21.28x = 31.85 × 13.64
  4. Step 4: Simplify right side
    21.28x = 434.54
  5. Step 5: Solve for x
    x = 434.54/21.28
  6. Step 6: Final answer
    x = 20.42

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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.