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Finding the Fourth Proportional to 81.20, 121.64 and 38.40

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Solution

The fourth proportional to 81.20, 121.64 and 38.40 is: 57.52

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.20 : 121.64 = 38.40 : x
  2. Step 2: Convert to fraction form
    81.20/121.64 = 38.40/x
  3. Step 3: Cross multiply
    81.20x = 121.64 × 38.40
  4. Step 4: Simplify right side
    81.20x = 4,670.98
  5. Step 5: Solve for x
    x = 4,670.98/81.20
  6. Step 6: Final answer
    x = 57.52

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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.