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Finding the Fourth Proportional to 100.78, 138.68 and 81.12

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Solution

The fourth proportional to 100.78, 138.68 and 81.12 is: 111.63

Step by Step Solution

  1. Step 1: Write the proportion equation
    100.78 : 138.68 = 81.12 : x
  2. Step 2: Convert to fraction form
    100.78/138.68 = 81.12/x
  3. Step 3: Cross multiply
    100.78x = 138.68 × 81.12
  4. Step 4: Simplify right side
    100.78x = 11,249.72
  5. Step 5: Solve for x
    x = 11,249.72/100.78
  6. Step 6: Final answer
    x = 111.63

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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.