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Finding the Fourth Proportional to 81, 120.86 and 72.90

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Solution

The fourth proportional to 81, 120.86 and 72.90 is: 108.77

Step by Step Solution

  1. Step 1: Write the proportion equation
    81 : 120.86 = 72.90 : x
  2. Step 2: Convert to fraction form
    81/120.86 = 72.90/x
  3. Step 3: Cross multiply
    81x = 120.86 × 72.90
  4. Step 4: Simplify right side
    81x = 8,810.69
  5. Step 5: Solve for x
    x = 8,810.69/81
  6. Step 6: Final answer
    x = 108.77

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Why These Related Problems?

These problems maintain the same ratio (1.49) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.