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Finding the Fourth Proportional to 81.68, 122.51 and 20.81

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Solution

The fourth proportional to 81.68, 122.51 and 20.81 is: 31.22

Step by Step Solution

  1. Step 1: Write the proportion equation
    81.68 : 122.51 = 20.81 : x
  2. Step 2: Convert to fraction form
    81.68/122.51 = 20.81/x
  3. Step 3: Cross multiply
    81.68x = 122.51 × 20.81
  4. Step 4: Simplify right side
    81.68x = 2,549.79
  5. Step 5: Solve for x
    x = 2,549.79/81.68
  6. Step 6: Final answer
    x = 31.22

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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.