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Finding the Fourth Proportional to 57.31, 85.90 and 21.20

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Solution

The fourth proportional to 57.31, 85.90 and 21.20 is: 31.78

Step by Step Solution

  1. Step 1: Write the proportion equation
    57.31 : 85.90 = 21.20 : x
  2. Step 2: Convert to fraction form
    57.31/85.90 = 21.20/x
  3. Step 3: Cross multiply
    57.31x = 85.90 × 21.20
  4. Step 4: Simplify right side
    57.31x = 1,821.08
  5. Step 5: Solve for x
    x = 1,821.08/57.31
  6. Step 6: Final answer
    x = 31.78

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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.