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Finding the Fourth Proportional to 81.21, 121.88 and 42.72

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Solution

The fourth proportional to 81.21, 121.88 and 42.72 is: 64.11

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.21 : 121.88 = 42.72 : x
  2. Step 2: Convert to fraction form
    81.21/121.88 = 42.72/x
  3. Step 3: Cross multiply
    81.21x = 121.88 × 42.72
  4. Step 4: Simplify right side
    81.21x = 5,206.44
  5. Step 5: Solve for x
    x = 5,206.44/81.21
  6. Step 6: Final answer
    x = 64.11

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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.