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Finding the Fourth Proportional to 21.20, 31.88 and 20.80

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Solution

The fourth proportional to 21.20, 31.88 and 20.80 is: 31.28

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.20 : 31.88 = 20.80 : x
  2. Step 2: Convert to fraction form
    21.20/31.88 = 20.80/x
  3. Step 3: Cross multiply
    21.20x = 31.88 × 20.80
  4. Step 4: Simplify right side
    21.20x = 663.10
  5. Step 5: Solve for x
    x = 663.10/21.20
  6. Step 6: Final answer
    x = 31.28

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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.