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Finding the Fourth Proportional to 100.45, 138.21 and 81.61

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Solution

The fourth proportional to 100.45, 138.21 and 81.61 is: 112.29

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.45 : 138.21 = 81.61 : x
  2. Step 2: Convert to fraction form
    100.45/138.21 = 81.61/x
  3. Step 3: Cross multiply
    100.45x = 138.21 × 81.61
  4. Step 4: Simplify right side
    100.45x = 11,279.32
  5. Step 5: Solve for x
    x = 11,279.32/100.45
  6. Step 6: Final answer
    x = 112.29

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Why These Related Problems?

These problems maintain the same ratio (1.38) or explore similar proportional relationships. Practicing with related ratios helps build understanding of proportional relationships.