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Finding the Fourth Proportional to 21.80, 30.90 and 21.80

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Solution

The fourth proportional to 21.80, 30.90 and 21.80 is: 30.90

Step by Step Solution

  1. Step 1: Write the proportion equation
    21.80 : 30.90 = 21.80 : x
  2. Step 2: Convert to fraction form
    21.80/30.90 = 21.80/x
  3. Step 3: Cross multiply
    21.80x = 30.90 × 21.80
  4. Step 4: Simplify right side
    21.80x = 673.62
  5. Step 5: Solve for x
    x = 673.62/21.80
  6. Step 6: Final answer
    x = 30.90

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Why These Related Problems?

These problems maintain the same ratio (1.42) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.